Migrate the IndexedDB backend from Blink to Chromium

content/browser/indexed_db/indexed_db_backing_store.cc

+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "content/browser/indexed_db/indexed_db_backing_store.h"
+
+#include <public/Platform.h>
+#include <public/WebIDBKey.h>
+#include <string>
+#include "base/file_util.h"
+#include "base/files/file_path.h"
+#include "base/logging.h"
+#include "base/metrics/histogram.h"
+#include "base/utf_string_conversions.h"
+#include "content/browser/indexed_db/indexed_db_leveldb_coding.h"
+#include "content/browser/indexed_db/indexed_db_metadata.h"
+#include "content/browser/indexed_db/indexed_db_tracing.h"
+#include "content/browser/indexed_db/leveldb/leveldb_comparator.h"
+#include "content/browser/indexed_db/leveldb/leveldb_database.h"
+#include "content/browser/indexed_db/leveldb/leveldb_iterator.h"
+#include "content/browser/indexed_db/leveldb/leveldb_slice.h"
+#include "content/browser/indexed_db/leveldb/leveldb_transaction.h"
+#include "content/common/indexed_db/indexed_db_key.h"
+#include "content/common/indexed_db/indexed_db_key_path.h"
+#include "content/common/indexed_db/indexed_db_key_range.h"
+#include "third_party/WebKit/Source/Platform/chromium/public/WebIDBKeyPath.h"
+
+// TODO: Make blink push the version during the open() call.
+static const uint32_t kWireVersion = 2;
+
+namespace content {
+
+using namespace IndexedDBLevelDBCoding;
+
+const int64_t KeyGeneratorInitialNumber =
+    1;  // From the IndexedDB specification.
+
+enum IndexedDBBackingStoreErrorSource {
+  // 0 - 2 are no longer used.
+  kFindKeyInIndex = 3,
+  kGetIDBDatabaseMetaData,
+  kGetIndexes,
+  kGetKeyGeneratorCurrentNumber,
+  kGetObjectStores,
+  kGetRecord,
+  kKeyExistsInObjectStore,
+  kLoadCurrentRow,
+  kSetupMetadata,
+  kGetPrimaryKeyViaIndex,
+  kKeyExistsInIndex,
+  kVersionExists,
+  kDeleteObjectStore,
+  kSetMaxObjectStoreId,
+  kSetMaxIndexId,
+  kGetNewDatabaseId,
+  kGetNewVersionNumber,
+  kCreateIDBDatabaseMetaData,
+  kDeleteDatabase,
+  kTransactionCommit,
+  kIndexedDBLevelDBBackingStoreInternalErrorMax,
+};
+
+static void RecordInternalError(const char* type,
+                                IndexedDBBackingStoreErrorSource location) {
+  string16 name = ASCIIToUTF16("WebCore.IndexedDB.BackingStore.") +
+                  UTF8ToUTF16(type) + ASCIIToUTF16("Error");
+  base::Histogram::FactoryGet(UTF16ToUTF8(name),
+                              1,
+                              kIndexedDBLevelDBBackingStoreInternalErrorMax,
+                              kIndexedDBLevelDBBackingStoreInternalErrorMax + 1,
+                              base::HistogramBase::kUmaTargetedHistogramFlag)
+      ->Add(location);
+}
+
+// Use to signal conditions that usually indicate developer error, but
+// could be caused by data corruption.  A macro is used instead of an
+// inline function so that the assert and log report the line number.
+#define REPORT_ERROR(type, location)                      \
+  do {                                                    \
+    LOG(ERROR) << "IndexedDB " type " Error: " #location; \
+    NOTREACHED();                                         \
+    RecordInternalError(type, location);                  \
+  } while (0)
+
+#define INTERNAL_READ_ERROR(location) REPORT_ERROR("Read", location)
+#define INTERNAL_CONSISTENCY_ERROR(location) \
+  REPORT_ERROR("Consistency", location)
+#define INTERNAL_WRITE_ERROR(location) REPORT_ERROR("Write", location)
+
+static void PutBool(LevelDBTransaction* transaction,
+                    const LevelDBSlice& key,
+                    bool value) {
+  transaction->Put(key, EncodeBool(value));
+}
+
+template <typename DBOrTransaction>
+static bool
+GetInt(DBOrTransaction* db,
+       const LevelDBSlice& key,
+       int64_t& found_int,
+       bool& found) {
+  std::vector<char> result;
+  bool ok = db->Get(key, result, found);
+  if (!ok)
+    return false;
+  if (!found)
+    return true;
+
+  found_int = DecodeInt(result.begin(), result.end());
+  return true;
+}
+
+static void PutInt(LevelDBTransaction* transaction,
+                   const LevelDBSlice& key,
+                   int64_t value) {
+  DCHECK_GE(value, 0);
+  transaction->Put(key, EncodeInt(value));
+}
+
+template <typename DBOrTransaction>
+WARN_UNUSED_RESULT static bool
+GetVarInt(DBOrTransaction* db,
+          const LevelDBSlice& key,
+          int64_t& found_int,
+          bool& found) {
+  std::vector<char> result;
+  bool ok = db->Get(key, result, found);
+  if (!ok)
+    return false;
+  if (!found)
+    return true;
+
+  found = DecodeVarInt(result.begin(), result.end(), found_int) == result.end();
+  return true;
+}
+
+static void PutVarInt(LevelDBTransaction* transaction,
+                      const LevelDBSlice& key,
+                      int64_t value) {
+  transaction->Put(key, EncodeVarInt(value));
+}
+
+template <typename DBOrTransaction>
+WARN_UNUSED_RESULT static bool
+GetString(DBOrTransaction* db,
+          const LevelDBSlice& key,
+          string16& found_string,
+          bool& found) {
+  std::vector<char> result;
+  found = false;
+  bool ok = db->Get(key, result, found);
+  if (!ok)
+    return false;
+  if (!found)
+    return true;
+
+  found_string = DecodeString(&result[0], &result[0] + result.size());
+  return true;
+}
+
+static void PutString(LevelDBTransaction* transaction,
+                      const LevelDBSlice& key,
+                      const string16& value) {
+  transaction->Put(key, EncodeString(value));
+}
+
+static void PutIDBKeyPath(LevelDBTransaction* transaction,
+                          const LevelDBSlice& key,
+                          const IndexedDBKeyPath& value) {
+  transaction->Put(key, EncodeIDBKeyPath(value));
+}
+
+static int CompareKeys(const LevelDBSlice& a, const LevelDBSlice& b) {
+  return Compare(a, b);
+}
+
+static int CompareIndexKeys(const LevelDBSlice& a, const LevelDBSlice& b) {
+  return Compare(a, b, true);
+}
+
+class Comparator : public LevelDBComparator {
+ public:
+  virtual int Compare(const LevelDBSlice& a, const LevelDBSlice& b) const
+      OVERRIDE {
+    return IndexedDBLevelDBCoding::Compare(a, b);
+  }
+  virtual const char* Name() const OVERRIDE { return "idb_cmp1"; }
+};
+
+// 0 - Initial version.
+// 1 - Adds UserIntVersion to DatabaseMetaData.
+// 2 - Adds DataVersion to to global metadata.
+const int64_t latest_known_schema_version = 2;
+WARN_UNUSED_RESULT static bool IsSchemaKnown(LevelDBDatabase* db, bool* known) {
+  int64_t db_schema_version = 0;
+  bool found = false;
+  bool ok = GetInt(
+      db, LevelDBSlice(SchemaVersionKey::Encode()), db_schema_version, found);
+  if (!ok)
+    return false;
+  if (!found) {
+    *known = true;
+    return true;
+  }
+  if (db_schema_version > latest_known_schema_version) {
+    *known = false;
+    return true;
+  }
+
+  const uint32_t latest_known_data_version = kWireVersion;
+  int64_t db_data_version = 0;
+  ok = GetInt(
+      db, LevelDBSlice(DataVersionKey::Encode()), db_data_version, found);
+  if (!ok)
+    return false;
+  if (!found) {
+    *known = true;
+    return true;
+  }
+
+  if (db_data_version > latest_known_data_version) {
+    *known = false;
+    return true;
+  }
+
+  *known = true;
+  return true;
+}
+
+WARN_UNUSED_RESULT static bool SetUpMetadata(LevelDBDatabase* db,
+                                             const string16& origin) {
+  const uint32_t latest_known_data_version = kWireVersion;
+  const std::vector<char> schema_version_key = SchemaVersionKey::Encode();
+  const std::vector<char> data_version_key = DataVersionKey::Encode();
+
+  scoped_refptr<LevelDBTransaction> transaction =
+      LevelDBTransaction::Create(db);
+
+  int64_t db_schema_version = 0;
+  int64_t db_data_version = 0;
+  bool found = false;
+  bool ok = GetInt(transaction.get(),
+                   LevelDBSlice(schema_version_key),
+                   db_schema_version,
+                   found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kSetupMetadata);
+    return false;
+  }
+  if (!found) {
+    // Initialize new backing store.
+    db_schema_version = latest_known_schema_version;
+    PutInt(
+        transaction.get(), LevelDBSlice(schema_version_key), db_schema_version);
+    db_data_version = latest_known_data_version;
+    PutInt(transaction.get(), LevelDBSlice(data_version_key), db_data_version);
+  } else {
+    // Upgrade old backing store.
+    DCHECK(db_schema_version <= latest_known_schema_version);
+    if (db_schema_version < 1) {
+      db_schema_version = 1;
+      PutInt(transaction.get(),
+             LevelDBSlice(schema_version_key),
+             db_schema_version);
+      const std::vector<char> start_key =
+          DatabaseNameKey::EncodeMinKeyForOrigin(origin);
+      const std::vector<char> stop_key =
+          DatabaseNameKey::EncodeStopKeyForOrigin(origin);
+      scoped_ptr<LevelDBIterator> it = db->CreateIterator();
+      for (it->Seek(LevelDBSlice(start_key));
+           it->IsValid() && CompareKeys(it->Key(), LevelDBSlice(stop_key)) < 0;
+           it->Next()) {
+        int64_t database_id = 0;
+        found = false;
+        bool ok = GetInt(transaction.get(), it->Key(), database_id, found);
+        if (!ok) {
+          INTERNAL_READ_ERROR(kSetupMetadata);
+          return false;
+        }
+        if (!found) {
+          INTERNAL_CONSISTENCY_ERROR(kSetupMetadata);
+          return false;
+        }
+        std::vector<char> int_version_key = DatabaseMetaDataKey::Encode(
+            database_id, DatabaseMetaDataKey::UserIntVersion);
+        PutVarInt(transaction.get(),
+                  LevelDBSlice(int_version_key),
+                  IndexedDBDatabaseMetadata::DefaultIntVersion);
+      }
+    }
+    if (db_schema_version < 2) {
+      db_schema_version = 2;
+      PutInt(transaction.get(),
+             LevelDBSlice(schema_version_key),
+             db_schema_version);
+      db_data_version = kWireVersion;
+      PutInt(
+          transaction.get(), LevelDBSlice(data_version_key), db_data_version);
+    }
+  }
+
+  // All new values will be written using this serialization version.
+  found = false;
+  ok = GetInt(transaction.get(),
+              LevelDBSlice(data_version_key),
+              db_data_version,
+              found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kSetupMetadata);
+    return false;
+  }
+  if (!found) {
+    INTERNAL_CONSISTENCY_ERROR(kSetupMetadata);
+    return false;
+  }
+  if (db_data_version < latest_known_data_version) {
+    db_data_version = latest_known_data_version;
+    PutInt(transaction.get(), LevelDBSlice(data_version_key), db_data_version);
+  }
+
+  DCHECK_EQ(db_schema_version, latest_known_schema_version);
+  DCHECK_EQ(db_data_version, latest_known_data_version);
+
+  if (!transaction->Commit()) {
+    INTERNAL_WRITE_ERROR(kSetupMetadata);
+    return false;
+  }
+  return true;
+}
+
+template <typename DBOrTransaction>
+WARN_UNUSED_RESULT static bool
+GetMaxObjectStoreId(DBOrTransaction* db,
+                    int64_t database_id,
+                    int64_t& max_object_store_id) {
+  const std::vector<char> max_object_store_id_key = DatabaseMetaDataKey::Encode(
+      database_id, DatabaseMetaDataKey::MaxObjectStoreId);
+  bool ok =
+      GetMaxObjectStoreId(db, max_object_store_id_key, max_object_store_id);
+  return ok;
+}
+
+template <typename DBOrTransaction>
+WARN_UNUSED_RESULT static bool
+GetMaxObjectStoreId(DBOrTransaction* db,
+                    const std::vector<char>& max_object_store_id_key,
+                    int64_t& max_object_store_id) {
+  max_object_store_id = -1;
+  bool found = false;
+  bool ok = GetInt(
+      db, LevelDBSlice(max_object_store_id_key), max_object_store_id, found);
+  if (!ok)
+    return false;
+  if (!found)
+    max_object_store_id = 0;
+
+  DCHECK_GE(max_object_store_id, 0);
+  return true;
+}
+
+class DefaultLevelDBFactory : public LevelDBFactory {
+ public:
+  virtual scoped_ptr<LevelDBDatabase> OpenLevelDB(
+      const string16& file_name,
+      const LevelDBComparator* comparator) OVERRIDE {
+    return LevelDBDatabase::Open(
+        base::FilePath::FromUTF8Unsafe(UTF16ToUTF8(file_name)), comparator);
+  }
+  virtual bool DestroyLevelDB(const string16& file_name) OVERRIDE {
+    return LevelDBDatabase::Destroy(
+        base::FilePath::FromUTF8Unsafe(UTF16ToUTF8(file_name)));
+  }
+};
+
+IndexedDBBackingStore::IndexedDBBackingStore(
+    const string16& identifier,
+    scoped_ptr<LevelDBDatabase> db,
+    scoped_ptr<LevelDBComparator> comparator)
+    : identifier_(identifier),
+      db_(db.Pass()),
+      comparator_(comparator.Pass()),
+      weak_factory_(this) {}
+
+IndexedDBBackingStore::~IndexedDBBackingStore() {
+  // db_'s destructor uses comparator_. The order of destruction is important.
+  db_.reset();
+  comparator_.reset();
+}
+
+IndexedDBBackingStore::RecordIdentifier::RecordIdentifier(
+    const std::vector<char>& primary_key,
+    int64_t version)
+    : primary_key_(primary_key), version_(version) {
+  DCHECK(!primary_key.empty());
+}
+IndexedDBBackingStore::RecordIdentifier::RecordIdentifier()
+    : primary_key_(), version_(-1) {}
+IndexedDBBackingStore::RecordIdentifier::~RecordIdentifier() {}
+
+IndexedDBBackingStore::Cursor::CursorOptions::CursorOptions() {}
+IndexedDBBackingStore::Cursor::CursorOptions::~CursorOptions() {}
+
+enum IndexedDBLevelDBBackingStoreOpenResult {
+  IndexedDBLevelDBBackingStoreOpenMemorySuccess,
+  IndexedDBLevelDBBackingStoreOpenSuccess,
+  IndexedDBLevelDBBackingStoreOpenFailedDirectory,
+  IndexedDBLevelDBBackingStoreOpenFailedUnknownSchema,
+  IndexedDBLevelDBBackingStoreOpenCleanupDestroyFailed,
+  IndexedDBLevelDBBackingStoreOpenCleanupReopenFailed,
+  IndexedDBLevelDBBackingStoreOpenCleanupReopenSuccess,
+  IndexedDBLevelDBBackingStoreOpenFailedIOErrCheckingSchema,
+  IndexedDBLevelDBBackingStoreOpenFailedUnknownErr,
+  IndexedDBLevelDBBackingStoreOpenMemoryFailed,
+  IndexedDBLevelDBBackingStoreOpenAttemptNonASCII,
+  IndexedDBLevelDBBackingStoreOpenMax,
+};
+
+scoped_refptr<IndexedDBBackingStore> IndexedDBBackingStore::Open(
+    const string16& database_identifier,
+    const string16& path_base_arg,
+    const string16& file_identifier) {
+  DefaultLevelDBFactory leveldb_factory;
+  return IndexedDBBackingStore::Open(
+      database_identifier, path_base_arg, file_identifier, &leveldb_factory);
+}
+
+scoped_refptr<IndexedDBBackingStore> IndexedDBBackingStore::Open(
+    const string16& database_identifier,
+    const string16& path_base_arg,
+    const string16& file_identifier,
+    LevelDBFactory* leveldb_factory) {
+  IDB_TRACE("IndexedDBBackingStore::open");
+  DCHECK(!path_base_arg.empty());
+  string16 path_base = path_base_arg;
+
+  scoped_ptr<LevelDBComparator> comparator(new Comparator());
+  scoped_ptr<LevelDBDatabase> db;
+
+  if (!IsStringASCII(path_base)) {
+    base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                                1,
+                                IndexedDBLevelDBBackingStoreOpenMax,
+                                IndexedDBLevelDBBackingStoreOpenMax + 1,
+                                base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(IndexedDBLevelDBBackingStoreOpenAttemptNonASCII);
+  }
+  base::FilePath file_path_base(UTF16ToUTF8(path_base));
+  if (!file_util::CreateDirectory(file_path_base)) {
+    LOG(ERROR) << "Unable to create IndexedDB database path " << path_base;
+    base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                                1,
+                                IndexedDBLevelDBBackingStoreOpenMax,
+                                IndexedDBLevelDBBackingStoreOpenMax + 1,
+                                base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(IndexedDBLevelDBBackingStoreOpenFailedDirectory);
+    return scoped_refptr<IndexedDBBackingStore>();
+  }
+
+  base::FilePath path_utf8 = file_path_base.Append(
+      UTF16ToUTF8(database_identifier) + ".indexeddb.leveldb");
+  string16 path_utf16 = UTF8ToUTF16(path_utf8.value());
+
+  db = leveldb_factory->OpenLevelDB(path_utf16, comparator.get());
+
+  if (db) {
+    bool known = false;
+    bool ok = IsSchemaKnown(db.get(), &known);
+    if (!ok) {
+      LOG(ERROR) << "IndexedDB had IO error checking schema, treating it as "
+                    "failure to open";
+      base::Histogram::FactoryGet(
+          "WebCore.IndexedDB.BackingStore.OpenStatus",
+          1,
+          IndexedDBLevelDBBackingStoreOpenMax,
+          IndexedDBLevelDBBackingStoreOpenMax + 1,
+          base::HistogramBase::kUmaTargetedHistogramFlag)
+          ->Add(IndexedDBLevelDBBackingStoreOpenFailedIOErrCheckingSchema);
+      db.reset();
+    } else if (!known) {
+      LOG(ERROR) << "IndexedDB backing store had unknown schema, treating it "
+                    "as failure to open";
+      base::Histogram::FactoryGet(
+          "WebCore.IndexedDB.BackingStore.OpenStatus",
+          1,
+          IndexedDBLevelDBBackingStoreOpenMax,
+          IndexedDBLevelDBBackingStoreOpenMax + 1,
+          base::HistogramBase::kUmaTargetedHistogramFlag)
+          ->Add(IndexedDBLevelDBBackingStoreOpenFailedUnknownSchema);
+      db.reset();
+    }
+  }
+
+  if (db) {
+    base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                                1,
+                                IndexedDBLevelDBBackingStoreOpenMax,
+                                IndexedDBLevelDBBackingStoreOpenMax + 1,
+                                base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(IndexedDBLevelDBBackingStoreOpenSuccess);
+  } else {
+    LOG(ERROR) << "IndexedDB backing store open failed, attempting cleanup";
+    bool success = leveldb_factory->DestroyLevelDB(path_utf16);
+    if (!success) {
+      LOG(ERROR) << "IndexedDB backing store cleanup failed";
+      base::Histogram::FactoryGet(
+          "WebCore.IndexedDB.BackingStore.OpenStatus",
+          1,
+          IndexedDBLevelDBBackingStoreOpenMax,
+          IndexedDBLevelDBBackingStoreOpenMax + 1,
+          base::HistogramBase::kUmaTargetedHistogramFlag)
+          ->Add(IndexedDBLevelDBBackingStoreOpenCleanupDestroyFailed);
+      return scoped_refptr<IndexedDBBackingStore>();
+    }
+
+    LOG(ERROR) << "IndexedDB backing store cleanup succeeded, reopening";
+    db = leveldb_factory->OpenLevelDB(path_utf16, comparator.get());
+    if (!db) {
+      LOG(ERROR) << "IndexedDB backing store reopen after recovery failed";
+      base::Histogram::FactoryGet(
+          "WebCore.IndexedDB.BackingStore.OpenStatus",
+          1,
+          IndexedDBLevelDBBackingStoreOpenMax,
+          IndexedDBLevelDBBackingStoreOpenMax + 1,
+          base::HistogramBase::kUmaTargetedHistogramFlag)
+          ->Add(IndexedDBLevelDBBackingStoreOpenCleanupReopenFailed);
+      return scoped_refptr<IndexedDBBackingStore>();
+    }
+    base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                                1,
+                                IndexedDBLevelDBBackingStoreOpenMax,
+                                IndexedDBLevelDBBackingStoreOpenMax + 1,
+                                base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(IndexedDBLevelDBBackingStoreOpenCleanupReopenSuccess);
+  }
+
+  if (!db) {
+    NOTREACHED();
+    base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                                1,
+                                IndexedDBLevelDBBackingStoreOpenMax,
+                                IndexedDBLevelDBBackingStoreOpenMax + 1,
+                                base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(IndexedDBLevelDBBackingStoreOpenFailedUnknownErr);
+    return scoped_refptr<IndexedDBBackingStore>();
+  }
+
+  return Create(file_identifier, db.Pass(), comparator.Pass());
+}
+
+scoped_refptr<IndexedDBBackingStore> IndexedDBBackingStore::OpenInMemory(
+    const string16& identifier) {
+  DefaultLevelDBFactory leveldb_factory;
+  return IndexedDBBackingStore::OpenInMemory(identifier, &leveldb_factory);
+}
+
+scoped_refptr<IndexedDBBackingStore> IndexedDBBackingStore::OpenInMemory(
+    const string16& identifier,
+    LevelDBFactory* leveldb_factory) {
+  IDB_TRACE("IndexedDBBackingStore::open_in_memory");
+
+  scoped_ptr<LevelDBComparator> comparator(new Comparator());
+  scoped_ptr<LevelDBDatabase> db =
+      LevelDBDatabase::OpenInMemory(comparator.get());
+  if (!db) {
+    LOG(ERROR) << "LevelDBDatabase::open_in_memory failed.";
+    base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                                1,
+                                IndexedDBLevelDBBackingStoreOpenMax,
+                                IndexedDBLevelDBBackingStoreOpenMax + 1,
+                                base::HistogramBase::kUmaTargetedHistogramFlag)
+        ->Add(IndexedDBLevelDBBackingStoreOpenMemoryFailed);
+    return scoped_refptr<IndexedDBBackingStore>();
+  }
+  base::Histogram::FactoryGet("WebCore.IndexedDB.BackingStore.OpenStatus",
+                              1,
+                              IndexedDBLevelDBBackingStoreOpenMax,
+                              IndexedDBLevelDBBackingStoreOpenMax + 1,
+                              base::HistogramBase::kUmaTargetedHistogramFlag)
+      ->Add(IndexedDBLevelDBBackingStoreOpenMemorySuccess);
+
+  return Create(identifier, db.Pass(), comparator.Pass());
+}
+
+scoped_refptr<IndexedDBBackingStore> IndexedDBBackingStore::Create(
+    const string16& identifier,
+    scoped_ptr<LevelDBDatabase> db,
+    scoped_ptr<LevelDBComparator> comparator) {
+  // TODO: Handle comparator name changes.
+  scoped_refptr<IndexedDBBackingStore> backing_store(
+      new IndexedDBBackingStore(identifier, db.Pass(), comparator.Pass()));
+
+  if (!SetUpMetadata(backing_store->db_.get(), identifier))
+    return scoped_refptr<IndexedDBBackingStore>();
+
+  return backing_store;
+}
+
+std::vector<string16> IndexedDBBackingStore::GetDatabaseNames() {
+  std::vector<string16> found_names;
+  const std::vector<char> start_key =
+      DatabaseNameKey::EncodeMinKeyForOrigin(identifier_);
+  const std::vector<char> stop_key =
+      DatabaseNameKey::EncodeStopKeyForOrigin(identifier_);
+
+  DCHECK(found_names.empty());
+
+  scoped_ptr<LevelDBIterator> it = db_->CreateIterator();
+  for (it->Seek(LevelDBSlice(start_key));
+       it->IsValid() && CompareKeys(it->Key(), LevelDBSlice(stop_key)) < 0;
+       it->Next()) {
+    const char* p = it->Key().begin();
+    const char* limit = it->Key().end();
+
+    DatabaseNameKey database_name_key;
+    p = DatabaseNameKey::Decode(p, limit, &database_name_key);
+    DCHECK(p);
+
+    found_names.push_back(database_name_key.database_name());
+  }
+  return found_names;
+}
+
+bool IndexedDBBackingStore::GetIDBDatabaseMetaData(
+    const string16& name,
+    IndexedDBDatabaseMetadata* metadata,
+    bool& found) {
+  const std::vector<char> key = DatabaseNameKey::Encode(identifier_, name);
+  found = false;
+
+  bool ok = GetInt(db_.get(), LevelDBSlice(key), metadata->id, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetIDBDatabaseMetaData);
+    return false;
+  }
+  if (!found)
+    return true;
+
+  ok = GetString(db_.get(),
+                 LevelDBSlice(DatabaseMetaDataKey::Encode(
+                     metadata->id, DatabaseMetaDataKey::UserVersion)),
+                 metadata->version,
+                 found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetIDBDatabaseMetaData);
+    return false;
+  }
+  if (!found) {
+    INTERNAL_CONSISTENCY_ERROR(kGetIDBDatabaseMetaData);
+    return false;
+  }
+
+  ok = GetVarInt(db_.get(),
+                 LevelDBSlice(DatabaseMetaDataKey::Encode(
+                     metadata->id, DatabaseMetaDataKey::UserIntVersion)),
+                 metadata->int_version,
+                 found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetIDBDatabaseMetaData);
+    return false;
+  }
+  if (!found) {
+    INTERNAL_CONSISTENCY_ERROR(kGetIDBDatabaseMetaData);
+    return false;
+  }
+
+  if (metadata->int_version == IndexedDBDatabaseMetadata::DefaultIntVersion)
+    metadata->int_version = IndexedDBDatabaseMetadata::NoIntVersion;
+
+  ok = GetMaxObjectStoreId(
+      db_.get(), metadata->id, metadata->max_object_store_id);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetIDBDatabaseMetaData);
+    return false;
+  }
+
+  return true;
+}
+
+WARN_UNUSED_RESULT static bool GetNewDatabaseId(LevelDBDatabase* db,
+                                                int64_t& new_id) {
+  scoped_refptr<LevelDBTransaction> transaction =
+      LevelDBTransaction::Create(db);
+
+  new_id = -1;
+  int64_t max_database_id = -1;
+  bool found = false;
+  bool ok = GetInt(transaction.get(),
+                   LevelDBSlice(MaxDatabaseIdKey::Encode()),
+                   max_database_id,
+                   found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetNewDatabaseId);
+    return false;
+  }
+  if (!found)
+    max_database_id = 0;
+
+  DCHECK_GE(max_database_id, 0);
+
+  int64_t database_id = max_database_id + 1;
+  PutInt(
+      transaction.get(), LevelDBSlice(MaxDatabaseIdKey::Encode()), database_id);
+  if (!transaction->Commit()) {
+    INTERNAL_WRITE_ERROR(kGetNewDatabaseId);
+    return false;
+  }
+  new_id = database_id;
+  return true;
+}
+
+bool IndexedDBBackingStore::CreateIDBDatabaseMetaData(const string16& name,
+                                                      const string16& version,
+                                                      int64_t int_version,
+                                                      int64_t& row_id) {
+  bool ok = GetNewDatabaseId(db_.get(), row_id);
+  if (!ok)
+    return false;
+  DCHECK_GE(row_id, 0);
+
+  if (int_version == IndexedDBDatabaseMetadata::NoIntVersion)
+    int_version = IndexedDBDatabaseMetadata::DefaultIntVersion;
+
+  scoped_refptr<LevelDBTransaction> transaction =
+      LevelDBTransaction::Create(db_.get());
+  PutInt(transaction.get(),
+         LevelDBSlice(DatabaseNameKey::Encode(identifier_, name)),
+         row_id);
+  PutString(transaction.get(),
+            LevelDBSlice(DatabaseMetaDataKey::Encode(
+                row_id, DatabaseMetaDataKey::UserVersion)),
+            version);
+  PutVarInt(transaction.get(),
+            LevelDBSlice(DatabaseMetaDataKey::Encode(
+                row_id, DatabaseMetaDataKey::UserIntVersion)),
+            int_version);
+  if (!transaction->Commit()) {
+    INTERNAL_WRITE_ERROR(kCreateIDBDatabaseMetaData);
+    return false;
+  }
+  return true;
+}
+
+bool IndexedDBBackingStore::UpdateIDBDatabaseIntVersion(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t row_id,
+    int64_t int_version) {
+  if (int_version == IndexedDBDatabaseMetadata::NoIntVersion)
+    int_version = IndexedDBDatabaseMetadata::DefaultIntVersion;
+  DCHECK_GE(int_version, 0) << "int_version was " << int_version;
+  PutVarInt(Transaction::LevelDBTransactionFrom(transaction),
+            LevelDBSlice(DatabaseMetaDataKey::Encode(
+                row_id, DatabaseMetaDataKey::UserIntVersion)),
+            int_version);
+  return true;
+}
+
+bool IndexedDBBackingStore::UpdateIDBDatabaseMetaData(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t row_id,
+    const string16& version) {
+  PutString(Transaction::LevelDBTransactionFrom(transaction),
+            LevelDBSlice(DatabaseMetaDataKey::Encode(
+                row_id, DatabaseMetaDataKey::UserVersion)),
+            version);
+  return true;
+}
+
+static void DeleteRange(LevelDBTransaction* transaction,
+                        const std::vector<char>& begin,
+                        const std::vector<char>& end) {
+  scoped_ptr<LevelDBIterator> it = transaction->CreateIterator();
+  for (it->Seek(LevelDBSlice(begin));
+       it->IsValid() && CompareKeys(it->Key(), LevelDBSlice(end)) < 0;
+       it->Next())
+    transaction->Remove(it->Key());
+}
+
+bool IndexedDBBackingStore::DeleteDatabase(const string16& name) {
+  IDB_TRACE("IndexedDBBackingStore::delete_database");
+  scoped_ptr<LevelDBWriteOnlyTransaction> transaction =
+      LevelDBWriteOnlyTransaction::Create(db_.get());
+
+  IndexedDBDatabaseMetadata metadata;
+  bool success = false;
+  bool ok = GetIDBDatabaseMetaData(name, &metadata, success);
+  if (!ok)
+    return false;
+  if (!success)
+    return true;
+
+  const std::vector<char> start_key =
+      DatabaseMetaDataKey::Encode(metadata.id, DatabaseMetaDataKey::OriginName);
+  const std::vector<char> stop_key = DatabaseMetaDataKey::Encode(
+      metadata.id + 1, DatabaseMetaDataKey::OriginName);
+  scoped_ptr<LevelDBIterator> it = db_->CreateIterator();
+  for (it->Seek(LevelDBSlice(start_key));
+       it->IsValid() && CompareKeys(it->Key(), LevelDBSlice(stop_key)) < 0;
+       it->Next())
+    transaction->Remove(it->Key());
+
+  const std::vector<char> key = DatabaseNameKey::Encode(identifier_, name);
+  transaction->Remove(LevelDBSlice(key));
+
+  if (!transaction->Commit()) {
+    INTERNAL_WRITE_ERROR(kDeleteDatabase);
+    return false;
+  }
+  return true;
+}
+
+static bool CheckObjectStoreAndMetaDataType(const LevelDBIterator* it,
+                                            const std::vector<char>& stop_key,
+                                            int64_t object_store_id,
+                                            int64_t meta_data_type) {
+  if (!it->IsValid() || CompareKeys(it->Key(), LevelDBSlice(stop_key)) >= 0)
+    return false;
+
+  ObjectStoreMetaDataKey meta_data_key;
+  const char* p = ObjectStoreMetaDataKey::Decode(
+      it->Key().begin(), it->Key().end(), &meta_data_key);
+  DCHECK(p);
+  if (meta_data_key.ObjectStoreId() != object_store_id)
+    return false;
+  if (meta_data_key.MetaDataType() != meta_data_type)
+    return false;
+  return true;
+}
+
+// TODO: This should do some error handling rather than plowing ahead when bad
+// data is encountered.
+bool IndexedDBBackingStore::GetObjectStores(
+    int64_t database_id,
+    IndexedDBDatabaseMetadata::ObjectStoreMap* object_stores) {
+  IDB_TRACE("IndexedDBBackingStore::get_object_stores");
+  if (!KeyPrefix::IsValidDatabaseId(database_id))
+    return false;
+  const std::vector<char> start_key =
+      ObjectStoreMetaDataKey::Encode(database_id, 1, 0);
+  const std::vector<char> stop_key =
+      ObjectStoreMetaDataKey::EncodeMaxKey(database_id);
+
+  DCHECK(object_stores->empty());
+
+  scoped_ptr<LevelDBIterator> it = db_->CreateIterator();
+  it->Seek(LevelDBSlice(start_key));
+  while (it->IsValid() && CompareKeys(it->Key(), LevelDBSlice(stop_key)) < 0) {
+    const char* p = it->Key().begin();
+    const char* limit = it->Key().end();
+
+    ObjectStoreMetaDataKey meta_data_key;
+    p = ObjectStoreMetaDataKey::Decode(p, limit, &meta_data_key);
+    DCHECK(p);
+    if (meta_data_key.MetaDataType() != ObjectStoreMetaDataKey::Name) {
+      INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+      // Possible stale metadata, but don't fail the load.
+      it->Next();
+      continue;
+    }
+
+    int64_t object_store_id = meta_data_key.ObjectStoreId();
+
+    // TODO: Do this by direct key lookup rather than iteration, to simplify.
+    string16 object_store_name =
+        DecodeString(it->Value().begin(), it->Value().end());
+
+    it->Next();
+    if (!CheckObjectStoreAndMetaDataType(it.get(),
+                                         stop_key,
+                                         object_store_id,
+                                         ObjectStoreMetaDataKey::KeyPath)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+      break;
+    }
+    IndexedDBKeyPath key_path =
+        DecodeIDBKeyPath(it->Value().begin(), it->Value().end());
+
+    it->Next();
+    if (!CheckObjectStoreAndMetaDataType(
+            it.get(),
+            stop_key,
+            object_store_id,
+            ObjectStoreMetaDataKey::AutoIncrement)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+      break;
+    }
+    bool auto_increment = DecodeBool(it->Value().begin(), it->Value().end());
+
+    it->Next();  // Is evicatble.
+    if (!CheckObjectStoreAndMetaDataType(it.get(),
+                                         stop_key,
+                                         object_store_id,
+                                         ObjectStoreMetaDataKey::Evictable)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+      break;
+    }
+
+    it->Next();  // Last version.
+    if (!CheckObjectStoreAndMetaDataType(it.get(),
+                                         stop_key,
+                                         object_store_id,
+                                         ObjectStoreMetaDataKey::LastVersion)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+      break;
+    }
+
+    it->Next();  // Maximum index id allocated.
+    if (!CheckObjectStoreAndMetaDataType(it.get(),
+                                         stop_key,
+                                         object_store_id,
+                                         ObjectStoreMetaDataKey::MaxIndexId)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+      break;
+    }
+    int64_t max_index_id = DecodeInt(it->Value().begin(), it->Value().end());
+
+    it->Next();  // [optional] has key path (is not null)
+    if (CheckObjectStoreAndMetaDataType(it.get(),
+                                        stop_key,
+                                        object_store_id,
+                                        ObjectStoreMetaDataKey::HasKeyPath)) {
+      bool has_key_path = DecodeBool(it->Value().begin(), it->Value().end());
+      // This check accounts for two layers of legacy coding:
+      // (1) Initially, has_key_path was added to distinguish null vs. string.
+      // (2) Later, null vs. string vs. array was stored in the key_path itself.
+      // So this check is only relevant for string-type key_paths.
+      if (!has_key_path &&
+          (key_path.type() == WebKit::WebIDBKeyPath::StringType &&
+           !key_path.string().empty())) {
+        INTERNAL_CONSISTENCY_ERROR(kGetObjectStores);
+        break;
+      }
+      if (!has_key_path)
+        key_path = IndexedDBKeyPath();
+      it->Next();
+    }
+
+    int64_t key_generator_current_number = -1;
+    if (CheckObjectStoreAndMetaDataType(
+            it.get(),
+            stop_key,
+            object_store_id,
+            ObjectStoreMetaDataKey::KeyGeneratorCurrentNumber)) {
+      key_generator_current_number =
+          DecodeInt(it->Value().begin(), it->Value().end());
+      // TODO: Return key_generator_current_number, cache in object store, and
+      // write lazily to backing store.
+      // For now, just assert that if it was written it was valid.
+      DCHECK_GE(key_generator_current_number, KeyGeneratorInitialNumber);
+      it->Next();
+    }
+
+    IndexedDBObjectStoreMetadata metadata(object_store_name,
+                                          object_store_id,
+                                          key_path,
+                                          auto_increment,
+                                          max_index_id);
+    if (!GetIndexes(database_id, object_store_id, &metadata.indexes))
+      return false;
+    (*object_stores)[object_store_id] = metadata;
+  }
+  return true;
+}
+
+WARN_UNUSED_RESULT static bool SetMaxObjectStoreId(
+    LevelDBTransaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id) {
+  const std::vector<char> max_object_store_id_key = DatabaseMetaDataKey::Encode(
+      database_id, DatabaseMetaDataKey::MaxObjectStoreId);
+  int64_t max_object_store_id = -1;
+  bool ok = GetMaxObjectStoreId(
+      transaction, max_object_store_id_key, max_object_store_id);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kSetMaxObjectStoreId);
+    return false;
+  }
+
+  if (object_store_id <= max_object_store_id) {
+    INTERNAL_CONSISTENCY_ERROR(kSetMaxObjectStoreId);
+    return false;
+  }
+  PutInt(transaction, LevelDBSlice(max_object_store_id_key), object_store_id);
+  return true;
+}
+
+bool IndexedDBBackingStore::CreateObjectStore(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const string16& name,
+    const IndexedDBKeyPath& key_path,
+    bool auto_increment) {
+  IDB_TRACE("IndexedDBBackingStore::create_object_store");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  if (!SetMaxObjectStoreId(leveldb_transaction, database_id, object_store_id))
+    return false;
+
+  const std::vector<char> name_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::Name);
+  const std::vector<char> key_path_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::KeyPath);
+  const std::vector<char> auto_increment_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::AutoIncrement);
+  const std::vector<char> evictable_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::Evictable);
+  const std::vector<char> last_version_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::LastVersion);
+  const std::vector<char> max_index_id_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::MaxIndexId);
+  const std::vector<char> has_key_path_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::HasKeyPath);
+  const std::vector<char> key_generator_current_number_key =
+      ObjectStoreMetaDataKey::Encode(
+          database_id,
+          object_store_id,
+          ObjectStoreMetaDataKey::KeyGeneratorCurrentNumber);
+  const std::vector<char> names_key =
+      ObjectStoreNamesKey::Encode(database_id, name);
+
+  PutString(leveldb_transaction, LevelDBSlice(name_key), name);
+  PutIDBKeyPath(leveldb_transaction, LevelDBSlice(key_path_key), key_path);
+  PutInt(leveldb_transaction, LevelDBSlice(auto_increment_key), auto_increment);
+  PutInt(leveldb_transaction, LevelDBSlice(evictable_key), false);
+  PutInt(leveldb_transaction, LevelDBSlice(last_version_key), 1);
+  PutInt(leveldb_transaction, LevelDBSlice(max_index_id_key), MinimumIndexId);
+  PutBool(
+      leveldb_transaction, LevelDBSlice(has_key_path_key), !key_path.IsNull());
+  PutInt(leveldb_transaction,
+         LevelDBSlice(key_generator_current_number_key),
+         KeyGeneratorInitialNumber);
+  PutInt(leveldb_transaction, LevelDBSlice(names_key), object_store_id);
+  return true;
+}
+
+bool IndexedDBBackingStore::DeleteObjectStore(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id) {
+  IDB_TRACE("IndexedDBBackingStore::delete_object_store");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+
+  string16 object_store_name;
+  bool found = false;
+  bool ok = GetString(
+      leveldb_transaction,
+      LevelDBSlice(ObjectStoreMetaDataKey::Encode(
+          database_id, object_store_id, ObjectStoreMetaDataKey::Name)),
+      object_store_name,
+      found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kDeleteObjectStore);
+    return false;
+  }
+  if (!found) {
+    INTERNAL_CONSISTENCY_ERROR(kDeleteObjectStore);
+    return false;
+  }
+
+  DeleteRange(
+      leveldb_transaction,
+      ObjectStoreMetaDataKey::Encode(database_id, object_store_id, 0),
+      ObjectStoreMetaDataKey::EncodeMaxKey(database_id, object_store_id));
+
+  leveldb_transaction->Remove(LevelDBSlice(
+      ObjectStoreNamesKey::Encode(database_id, object_store_name)));
+
+  DeleteRange(leveldb_transaction,
+              IndexFreeListKey::Encode(database_id, object_store_id, 0),
+              IndexFreeListKey::EncodeMaxKey(database_id, object_store_id));
+  DeleteRange(leveldb_transaction,
+              IndexMetaDataKey::Encode(database_id, object_store_id, 0, 0),
+              IndexMetaDataKey::EncodeMaxKey(database_id, object_store_id));
+
+  return ClearObjectStore(transaction, database_id, object_store_id);
+}
+
+bool IndexedDBBackingStore::GetRecord(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const IndexedDBKey& key,
+    std::vector<char>& record) {
+  IDB_TRACE("IndexedDBBackingStore::get_record");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+
+  const std::vector<char> leveldb_key =
+      ObjectStoreDataKey::Encode(database_id, object_store_id, key);
+  std::vector<char> data;
+
+  record.clear();
+
+  bool found = false;
+  bool ok = leveldb_transaction->Get(LevelDBSlice(leveldb_key), data, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetRecord);
+    return false;
+  }
+  if (!found)
+    return true;
+
+  int64_t version;
+  std::vector<char>::iterator p =
+      DecodeVarInt(data.begin(), data.end(), version);
+  if (p == data.begin()) {
+    INTERNAL_READ_ERROR(kGetRecord);
+    return false;
+  }
+
+  record.assign(p, data.end());
+  return true;
+}
+
+WARN_UNUSED_RESULT static bool GetNewVersionNumber(
+    LevelDBTransaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t& new_version_number) {
+  const std::vector<char> last_version_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::LastVersion);
+
+  new_version_number = -1;
+  int64_t last_version = -1;
+  bool found = false;
+  bool ok =
+      GetInt(transaction, LevelDBSlice(last_version_key), last_version, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetNewVersionNumber);
+    return false;
+  }
+  if (!found)
+    last_version = 0;
+
+  DCHECK_GE(last_version, 0);
+
+  int64_t version = last_version + 1;
+  PutInt(transaction, LevelDBSlice(last_version_key), version);
+
+  DCHECK(version > last_version);  // TODO: Think about how we want to handle
+                                   // the overflow scenario.
+
+  new_version_number = version;
+  return true;
+}
+
+bool IndexedDBBackingStore::PutRecord(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const IndexedDBKey& key,
+    const std::vector<char>& value,
+    RecordIdentifier* record_identifier) {
+  IDB_TRACE("IndexedDBBackingStore::put_record");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  DCHECK(key.IsValid());
+
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  int64_t version = -1;
+  bool ok = GetNewVersionNumber(
+      leveldb_transaction, database_id, object_store_id, version);
+  if (!ok)
+    return false;
+  DCHECK_GE(version, 0);
+  const std::vector<char> object_storedata_key =
+      ObjectStoreDataKey::Encode(database_id, object_store_id, key);
+
+  std::vector<char> v(EncodeVarInt(version));
+
+  v.insert(v.end(), value.begin(), value.end());
+
+  leveldb_transaction->Put(LevelDBSlice(object_storedata_key), v);
+
+  const std::vector<char> exists_entry_key =
+      ExistsEntryKey::Encode(database_id, object_store_id, key);
+  leveldb_transaction->Put(LevelDBSlice(exists_entry_key), EncodeInt(version));
+
+  record_identifier->Reset(EncodeIDBKey(key), version);
+  return true;
+}
+
+bool IndexedDBBackingStore::ClearObjectStore(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id) {
+  IDB_TRACE("IndexedDBBackingStore::clear_object_store");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  const std::vector<char> start_key =
+      KeyPrefix(database_id, object_store_id).Encode();
+  const std::vector<char> stop_key =
+      KeyPrefix(database_id, object_store_id + 1).Encode();
+
+  DeleteRange(leveldb_transaction, start_key, stop_key);
+  return true;
+}
+
+bool IndexedDBBackingStore::DeleteRecord(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const RecordIdentifier& record_identifier) {
+  IDB_TRACE("IndexedDBBackingStore::delete_record");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+
+  const std::vector<char> object_store_data_key = ObjectStoreDataKey::Encode(
+      database_id, object_store_id, record_identifier.primary_key());
+  leveldb_transaction->Remove(LevelDBSlice(object_store_data_key));
+
+  const std::vector<char> exists_entry_key = ExistsEntryKey::Encode(
+      database_id, object_store_id, record_identifier.primary_key());
+  leveldb_transaction->Remove(LevelDBSlice(exists_entry_key));
+  return true;
+}
+
+bool IndexedDBBackingStore::GetKeyGeneratorCurrentNumber(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t& key_generator_current_number) {
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+
+  const std::vector<char> key_generator_current_number_key =
+      ObjectStoreMetaDataKey::Encode(
+          database_id,
+          object_store_id,
+          ObjectStoreMetaDataKey::KeyGeneratorCurrentNumber);
+
+  key_generator_current_number = -1;
+  std::vector<char> data;
+
+  bool found = false;
+  bool ok = leveldb_transaction->Get(
+      LevelDBSlice(key_generator_current_number_key), data, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetKeyGeneratorCurrentNumber);
+    return false;
+  }
+  if (found) {
+    key_generator_current_number = DecodeInt(data.begin(), data.end());
+  } else {
+    // Previously, the key generator state was not stored explicitly
+    // but derived from the maximum numeric key present in existing
+    // data. This violates the spec as the data may be cleared but the
+    // key generator state must be preserved.
+    const std::vector<char> start_key =
+        ObjectStoreDataKey::Encode(database_id, object_store_id, MinIDBKey());
+    const std::vector<char> stop_key =
+        ObjectStoreDataKey::Encode(database_id, object_store_id, MaxIDBKey());
+
+    scoped_ptr<LevelDBIterator> it = leveldb_transaction->CreateIterator();
+    int64_t max_numeric_key = 0;
+
+    for (it->Seek(LevelDBSlice(start_key));
+         it->IsValid() && CompareKeys(it->Key(), LevelDBSlice(stop_key)) < 0;
+         it->Next()) {
+      const char* p = it->Key().begin();
+      const char* limit = it->Key().end();
+
+      ObjectStoreDataKey data_key;
+      p = ObjectStoreDataKey::Decode(p, limit, &data_key);
+      DCHECK(p);
+
+      scoped_ptr<IndexedDBKey> user_key = data_key.user_key();
+      if (user_key->type() == WebKit::WebIDBKey::NumberType) {
+        int64_t n = static_cast<int64_t>(user_key->number());
+        if (n > max_numeric_key)
+          max_numeric_key = n;
+      }
+    }
+
+    key_generator_current_number = max_numeric_key + 1;
+  }
+
+  return key_generator_current_number;
+}
+
+bool IndexedDBBackingStore::MaybeUpdateKeyGeneratorCurrentNumber(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t new_number,
+    bool check_current) {
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+
+  if (check_current) {
+    int64_t current_number;
+    bool ok = GetKeyGeneratorCurrentNumber(
+        transaction, database_id, object_store_id, current_number);
+    if (!ok)
+      return false;
+    if (new_number <= current_number)
+      return true;
+  }
+
+  const std::vector<char> key_generator_current_number_key =
+      ObjectStoreMetaDataKey::Encode(
+          database_id,
+          object_store_id,
+          ObjectStoreMetaDataKey::KeyGeneratorCurrentNumber);
+  PutInt(leveldb_transaction,
+         LevelDBSlice(key_generator_current_number_key),
+         new_number);
+  return true;
+}
+
+bool IndexedDBBackingStore::KeyExistsInObjectStore(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const IndexedDBKey& key,
+    RecordIdentifier* found_record_identifier,
+    bool& found) {
+  IDB_TRACE("IndexedDBBackingStore::key_exists_in_object_store");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  found = false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  const std::vector<char> leveldb_key =
+      ObjectStoreDataKey::Encode(database_id, object_store_id, key);
+  std::vector<char> data;
+
+  bool ok = leveldb_transaction->Get(LevelDBSlice(leveldb_key), data, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kKeyExistsInObjectStore);
+    return false;
+  }
+  if (!found)
+    return true;
+
+  int64_t version;
+  if (DecodeVarInt(data.begin(), data.end(), version) == data.begin())
+    return false;
+
+  found_record_identifier->Reset(EncodeIDBKey(key), version);
+  return true;
+}
+
+static bool CheckIndexAndMetaDataKey(const LevelDBIterator* it,
+                                     const std::vector<char>& stop_key,
+                                     int64_t index_id,
+                                     unsigned char meta_data_type) {
+  if (!it->IsValid() || CompareKeys(it->Key(), LevelDBSlice(stop_key)) >= 0)
+    return false;
+
+  IndexMetaDataKey meta_data_key;
+  const char* p = IndexMetaDataKey::Decode(
+      it->Key().begin(), it->Key().end(), &meta_data_key);
+  DCHECK(p);
+  if (meta_data_key.IndexId() != index_id)
+    return false;
+  if (meta_data_key.meta_data_type() != meta_data_type)
+    return false;
+  return true;
+}
+
+// TODO: This should do some error handling rather than plowing ahead when bad
+// data is encountered.
+bool IndexedDBBackingStore::GetIndexes(
+    int64_t database_id,
+    int64_t object_store_id,
+    IndexedDBObjectStoreMetadata::IndexMap* indexes) {
+  IDB_TRACE("IndexedDBBackingStore::get_indexes");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id))
+    return false;
+  const std::vector<char> start_key =
+      IndexMetaDataKey::Encode(database_id, object_store_id, 0, 0);
+  const std::vector<char> stop_key =
+      IndexMetaDataKey::Encode(database_id, object_store_id + 1, 0, 0);
+
+  DCHECK(indexes->empty());
+
+  scoped_ptr<LevelDBIterator> it = db_->CreateIterator();
+  it->Seek(LevelDBSlice(start_key));
+  while (it->IsValid() &&
+         CompareKeys(LevelDBSlice(it->Key()), LevelDBSlice(stop_key)) < 0) {
+    const char* p = it->Key().begin();
+    const char* limit = it->Key().end();
+
+    IndexMetaDataKey meta_data_key;
+    p = IndexMetaDataKey::Decode(p, limit, &meta_data_key);
+    DCHECK(p);
+    if (meta_data_key.meta_data_type() != IndexMetaDataKey::Name) {
+      INTERNAL_CONSISTENCY_ERROR(kGetIndexes);
+      // Possible stale metadata due to http://webkit.org/b/85557 but don't fail
+      // the load.
+      it->Next();
+      continue;
+    }
+
+    // TODO: Do this by direct key lookup rather than iteration, to simplify.
+    int64_t index_id = meta_data_key.IndexId();
+    string16 index_name = DecodeString(it->Value().begin(), it->Value().end());
+
+    it->Next();  // unique flag
+    if (!CheckIndexAndMetaDataKey(
+            it.get(), stop_key, index_id, IndexMetaDataKey::Unique)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetIndexes);
+      break;
+    }
+    bool index_unique = DecodeBool(it->Value().begin(), it->Value().end());
+
+    it->Next();  // key_path
+    if (!CheckIndexAndMetaDataKey(
+            it.get(), stop_key, index_id, IndexMetaDataKey::KeyPath)) {
+      INTERNAL_CONSISTENCY_ERROR(kGetIndexes);
+      break;
+    }
+    IndexedDBKeyPath key_path =
+        DecodeIDBKeyPath(it->Value().begin(), it->Value().end());
+
+    it->Next();  // [optional] multi_entry flag
+    bool index_multi_entry = false;
+    if (CheckIndexAndMetaDataKey(
+            it.get(), stop_key, index_id, IndexMetaDataKey::MultiEntry)) {
+      index_multi_entry = DecodeBool(it->Value().begin(), it->Value().end());
+      it->Next();
+    }
+
+    (*indexes)[index_id] = IndexedDBIndexMetadata(
+        index_name, index_id, key_path, index_unique, index_multi_entry);
+  }
+  return true;
+}
+
+WARN_UNUSED_RESULT static bool SetMaxIndexId(LevelDBTransaction* transaction,
+                                             int64_t database_id,
+                                             int64_t object_store_id,
+                                             int64_t index_id) {
+  int64_t max_index_id = -1;
+  const std::vector<char> max_index_id_key = ObjectStoreMetaDataKey::Encode(
+      database_id, object_store_id, ObjectStoreMetaDataKey::MaxIndexId);
+  bool found = false;
+  bool ok =
+      GetInt(transaction, LevelDBSlice(max_index_id_key), max_index_id, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kSetMaxIndexId);
+    return false;
+  }
+  if (!found)
+    max_index_id = MinimumIndexId;
+
+  if (index_id <= max_index_id) {
+    INTERNAL_CONSISTENCY_ERROR(kSetMaxIndexId);
+    return false;
+  }
+
+  PutInt(transaction, LevelDBSlice(max_index_id_key), index_id);
+  return true;
+}
+
+bool IndexedDBBackingStore::CreateIndex(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const string16& name,
+    const IndexedDBKeyPath& key_path,
+    bool is_unique,
+    bool is_multi_entry) {
+  IDB_TRACE("IndexedDBBackingStore::create_index");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id, index_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  if (!SetMaxIndexId(
+          leveldb_transaction, database_id, object_store_id, index_id))
+    return false;
+
+  const std::vector<char> name_key = IndexMetaDataKey::Encode(
+      database_id, object_store_id, index_id, IndexMetaDataKey::Name);
+  const std::vector<char> unique_key = IndexMetaDataKey::Encode(
+      database_id, object_store_id, index_id, IndexMetaDataKey::Unique);
+  const std::vector<char> key_path_key = IndexMetaDataKey::Encode(
+      database_id, object_store_id, index_id, IndexMetaDataKey::KeyPath);
+  const std::vector<char> multi_entry_key = IndexMetaDataKey::Encode(
+      database_id, object_store_id, index_id, IndexMetaDataKey::MultiEntry);
+
+  PutString(leveldb_transaction, LevelDBSlice(name_key), name);
+  PutBool(leveldb_transaction, LevelDBSlice(unique_key), is_unique);
+  PutIDBKeyPath(leveldb_transaction, LevelDBSlice(key_path_key), key_path);
+  PutBool(leveldb_transaction, LevelDBSlice(multi_entry_key), is_multi_entry);
+  return true;
+}
+
+bool IndexedDBBackingStore::DeleteIndex(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id) {
+  IDB_TRACE("IndexedDBBackingStore::delete_index");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id, index_id))
+    return false;
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+
+  const std::vector<char> index_meta_data_start =
+      IndexMetaDataKey::Encode(database_id, object_store_id, index_id, 0);
+  const std::vector<char> index_meta_data_end =
+      IndexMetaDataKey::EncodeMaxKey(database_id, object_store_id, index_id);
+  DeleteRange(leveldb_transaction, index_meta_data_start, index_meta_data_end);
+
+  const std::vector<char> index_data_start =
+      IndexDataKey::EncodeMinKey(database_id, object_store_id, index_id);
+  const std::vector<char> index_data_end =
+      IndexDataKey::EncodeMaxKey(database_id, object_store_id, index_id);
+  DeleteRange(leveldb_transaction, index_data_start, index_data_end);
+  return true;
+}
+
+bool IndexedDBBackingStore::PutIndexDataForRecord(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKey& key,
+    const RecordIdentifier& record_identifier) {
+  IDB_TRACE("IndexedDBBackingStore::put_index_data_for_record");
+  DCHECK(key.IsValid());
+  if (!KeyPrefix::ValidIds(database_id, object_store_id, index_id))
+    return false;
+
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  const std::vector<char> index_data_key =
+      IndexDataKey::Encode(database_id,
+                           object_store_id,
+                           index_id,
+                           EncodeIDBKey(key),
+                           record_identifier.primary_key());
+
+  std::vector<char> data(EncodeVarInt(record_identifier.version()));
+  const std::vector<char>& primary_key = record_identifier.primary_key();
+  data.insert(data.end(), primary_key.begin(), primary_key.end());
+
+  leveldb_transaction->Put(LevelDBSlice(index_data_key), data);
+  return true;
+}
+
+static bool FindGreatestKeyLessThanOrEqual(LevelDBTransaction* transaction,
+                                           const std::vector<char>& target,
+                                           std::vector<char>& found_key) {
+  scoped_ptr<LevelDBIterator> it = transaction->CreateIterator();
+  it->Seek(LevelDBSlice(target));
+
+  if (!it->IsValid()) {
+    it->SeekToLast();
+    if (!it->IsValid())
+      return false;
+  }
+
+  while (CompareIndexKeys(LevelDBSlice(it->Key()), LevelDBSlice(target)) > 0) {
+    it->Prev();
+    if (!it->IsValid())
+      return false;
+  }
+
+  do {
+    found_key.assign(it->Key().begin(), it->Key().end());
+
+    // There can be several index keys that compare equal. We want the last one.
+    it->Next();
+  } while (it->IsValid() && !CompareIndexKeys(it->Key(), LevelDBSlice(target)));
+
+  return true;
+}
+
+static bool VersionExists(LevelDBTransaction* transaction,
+                          int64_t database_id,
+                          int64_t object_store_id,
+                          int64_t version,
+                          const std::vector<char>& encoded_primary_key,
+                          bool& exists) {
+  const std::vector<char> key =
+      ExistsEntryKey::Encode(database_id, object_store_id, encoded_primary_key);
+  std::vector<char> data;
+
+  bool ok = transaction->Get(LevelDBSlice(key), data, exists);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kVersionExists);
+    return false;
+  }
+  if (!exists)
+    return true;
+
+  exists = (DecodeInt(data.begin(), data.end()) == version);
+  return true;
+}
+
+bool IndexedDBBackingStore::FindKeyInIndex(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKey& key,
+    std::vector<char>& found_encoded_primary_key,
+    bool& found) {
+  IDB_TRACE("IndexedDBBackingStore::find_key_in_index");
+  DCHECK(KeyPrefix::ValidIds(database_id, object_store_id, index_id));
+
+  DCHECK(found_encoded_primary_key.empty());
+  found = false;
+
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  const std::vector<char> leveldb_key =
+      IndexDataKey::Encode(database_id, object_store_id, index_id, key);
+  scoped_ptr<LevelDBIterator> it = leveldb_transaction->CreateIterator();
+  it->Seek(LevelDBSlice(leveldb_key));
+
+  for (;;) {
+    if (!it->IsValid())
+      return true;
+    if (CompareIndexKeys(it->Key(), LevelDBSlice(leveldb_key)) > 0)
+      return true;
+
+    int64_t version;
+    const char* p =
+        DecodeVarInt(it->Value().begin(), it->Value().end(), version);
+    if (!p) {
+      INTERNAL_READ_ERROR(kFindKeyInIndex);
+      return false;
+    }
+    found_encoded_primary_key.insert(
+        found_encoded_primary_key.end(), p, it->Value().end());
+
+    bool exists = false;
+    bool ok = VersionExists(leveldb_transaction,
+                            database_id,
+                            object_store_id,
+                            version,
+                            found_encoded_primary_key,
+                            exists);
+    if (!ok)
+      return false;
+    if (!exists) {
+      // Delete stale index data entry and continue.
+      leveldb_transaction->Remove(it->Key());
+      it->Next();
+      continue;
+    }
+    found = true;
+    return true;
+  }
+}
+
+bool IndexedDBBackingStore::GetPrimaryKeyViaIndex(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKey& key,
+    scoped_ptr<IndexedDBKey>* primary_key) {
+  IDB_TRACE("IndexedDBBackingStore::get_primary_key_via_index");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id, index_id))
+    return false;
+
+  bool found = false;
+  std::vector<char> found_encoded_primary_key;
+  bool ok = FindKeyInIndex(transaction,
+                           database_id,
+                           object_store_id,
+                           index_id,
+                           key,
+                           found_encoded_primary_key,
+                           found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kGetPrimaryKeyViaIndex);
+    return false;
+  }
+  if (found) {
+    DecodeIDBKey(&*found_encoded_primary_key.begin(),
+                 &*found_encoded_primary_key.end(),
+                 primary_key);
+    return true;
+  }
+
+  return true;
+}
+
+bool IndexedDBBackingStore::KeyExistsInIndex(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKey& index_key,
+    scoped_ptr<IndexedDBKey>* found_primary_key,
+    bool& exists) {
+  IDB_TRACE("IndexedDBBackingStore::key_exists_in_index");
+  if (!KeyPrefix::ValidIds(database_id, object_store_id, index_id))
+    return false;
+
+  exists = false;
+  std::vector<char> found_encoded_primary_key;
+  bool ok = FindKeyInIndex(transaction,
+                           database_id,
+                           object_store_id,
+                           index_id,
+                           index_key,
+                           found_encoded_primary_key,
+                           exists);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kKeyExistsInIndex);
+    return false;
+  }
+  if (!exists)
+    return true;
+
+  DecodeIDBKey(&*found_encoded_primary_key.begin(),
+               &*found_encoded_primary_key.end(),
+               found_primary_key);
+  return true;
+}
+
+IndexedDBBackingStore::Cursor::Cursor(
+    const IndexedDBBackingStore::Cursor* other)
+    : transaction_(other->transaction_),
+      cursor_options_(other->cursor_options_),
+      current_key_(new IndexedDBKey(*other->current_key_)) {
+  if (other->iterator_) {
+    iterator_ = transaction_->CreateIterator();
+
+    if (other->iterator_->IsValid()) {
+      iterator_->Seek(other->iterator_->Key());
+      DCHECK(iterator_->IsValid());
+    }
+  }
+}
+
+IndexedDBBackingStore::Cursor::Cursor(LevelDBTransaction* transaction,
+                                      const CursorOptions& cursor_options)
+    : transaction_(transaction), cursor_options_(cursor_options) {}
+IndexedDBBackingStore::Cursor::~Cursor() {}
+
+bool IndexedDBBackingStore::Cursor::FirstSeek() {
+  iterator_ = transaction_->CreateIterator();
+  if (cursor_options_.forward)
+    iterator_->Seek(LevelDBSlice(cursor_options_.low_key));
+  else
+    iterator_->Seek(LevelDBSlice(cursor_options_.high_key));
+
+  return ContinueFunction(0, Ready);
+}
+
+bool IndexedDBBackingStore::Cursor::Advance(unsigned long count) {
+  while (count--) {
+    if (!ContinueFunction())
+      return false;
+  }
+  return true;
+}
+
+bool IndexedDBBackingStore::Cursor::ContinueFunction(const IndexedDBKey* key,
+                                                     IteratorState next_state) {
+  // TODO(alecflett): avoid a copy here?
+  IndexedDBKey previous_key = current_key_ ? *current_key_ : IndexedDBKey();
+
+  bool first_iteration = true;
+
+  // When iterating with PrevNoDuplicate, spec requires that the
+  // value we yield for each key is the first duplicate in forwards
+  // order.
+  IndexedDBKey last_duplicate_key;
+
+  bool forward = cursor_options_.forward;
+
+  for (;;) {
+    if (next_state == Seek) {
+      // TODO: Optimize seeking for reverse cursors as well.
+      if (first_iteration && key && key->IsValid() && forward) {
+        iterator_->Seek(LevelDBSlice(EncodeKey(*key)));
+        first_iteration = false;
+      } else if (forward) {
+        iterator_->Next();
+      } else {
+        iterator_->Prev();
+      }
+    } else {
+      next_state = Seek;  // for subsequent iterations
+    }
+
+    if (!iterator_->IsValid()) {
+      if (!forward && last_duplicate_key.IsValid()) {
+        // We need to walk forward because we hit the end of
+        // the data.
+        forward = true;
+        continue;
+      }
+
+      return false;
+    }
+
+    if (IsPastBounds()) {
+      if (!forward && last_duplicate_key.IsValid()) {
+        // We need to walk forward because now we're beyond the
+        // bounds defined by the cursor.
+        forward = true;
+        continue;
+      }
+
+      return false;
+    }
+
+    if (!HaveEnteredRange())
+      continue;
+
+    // The row may not load because there's a stale entry in the
+    // index. This is not fatal.
+    if (!LoadCurrentRow())
+      continue;
+
+    if (key && key->IsValid()) {
+      if (forward) {
+        if (current_key_->IsLessThan(*key))
+          continue;
+      } else {
+        if (key->IsLessThan(*current_key_))
+          continue;
+      }
+    }
+
+    if (cursor_options_.unique) {
+      if (previous_key.IsValid() && current_key_->IsEqual(previous_key)) {
+        // We should never be able to walk forward all the way
+        // to the previous key.
+        DCHECK(!last_duplicate_key.IsValid());
+        continue;
+      }
+
+      if (!forward) {
+        if (!last_duplicate_key.IsValid()) {
+          last_duplicate_key = *current_key_;
+          continue;
+        }
+
+        // We need to walk forward because we hit the boundary
+        // between key ranges.
+        if (!last_duplicate_key.IsEqual(*current_key_)) {
+          forward = true;
+          continue;
+        }
+
+        continue;
+      }
+    }
+    break;
+  }
+
+  DCHECK(!last_duplicate_key.IsValid() ||
+         (forward && last_duplicate_key.IsEqual(*current_key_)));
+  return true;
+}
+
+bool IndexedDBBackingStore::Cursor::HaveEnteredRange() const {
+  if (cursor_options_.forward) {
+    if (cursor_options_.low_open)
+      return CompareIndexKeys(iterator_->Key(),
+                              LevelDBSlice(cursor_options_.low_key)) >
+             0;
+
+    return CompareIndexKeys(iterator_->Key(),
+                            LevelDBSlice(cursor_options_.low_key)) >=
+           0;
+  }
+  if (cursor_options_.high_open)
+    return CompareIndexKeys(iterator_->Key(),
+                            LevelDBSlice(cursor_options_.high_key)) <
+           0;
+
+  return CompareIndexKeys(iterator_->Key(),
+                          LevelDBSlice(cursor_options_.high_key)) <=
+         0;
+}
+
+bool IndexedDBBackingStore::Cursor::IsPastBounds() const {
+  if (cursor_options_.forward) {
+    if (cursor_options_.high_open)
+      return CompareIndexKeys(iterator_->Key(),
+                              LevelDBSlice(cursor_options_.high_key)) >=
+             0;
+    return CompareIndexKeys(iterator_->Key(),
+                            LevelDBSlice(cursor_options_.high_key)) >
+           0;
+  }
+
+  if (cursor_options_.low_open)
+    return CompareIndexKeys(iterator_->Key(),
+                            LevelDBSlice(cursor_options_.low_key)) <=
+           0;
+  return CompareIndexKeys(iterator_->Key(),
+                          LevelDBSlice(cursor_options_.low_key)) <
+         0;
+}
+
+const IndexedDBKey& IndexedDBBackingStore::Cursor::primary_key() const {
+  return *current_key_;
+}
+
+const IndexedDBBackingStore::RecordIdentifier&
+IndexedDBBackingStore::Cursor::record_identifier() const {
+  return record_identifier_;
+}
+
+class ObjectStoreKeyCursorImpl : public IndexedDBBackingStore::Cursor {
+ public:
+  ObjectStoreKeyCursorImpl(
+      LevelDBTransaction* transaction,
+      const IndexedDBBackingStore::Cursor::CursorOptions& cursor_options)
+      : IndexedDBBackingStore::Cursor(transaction, cursor_options) {}
+
+  virtual Cursor* Clone() OVERRIDE {
+    return new ObjectStoreKeyCursorImpl(this);
+  }
+
+  // IndexedDBBackingStore::Cursor
+  virtual std::vector<char>* Value() OVERRIDE {
+    NOTREACHED();
+    return NULL;
+  }
+  virtual bool LoadCurrentRow() OVERRIDE;
+
+ protected:
+  virtual std::vector<char> EncodeKey(const IndexedDBKey& key) OVERRIDE {
+    return ObjectStoreDataKey::Encode(
+        cursor_options_.database_id, cursor_options_.object_store_id, key);
+  }
+
+ private:
+  explicit ObjectStoreKeyCursorImpl(const ObjectStoreKeyCursorImpl* other)
+      : IndexedDBBackingStore::Cursor(other) {}
+};
+
+bool ObjectStoreKeyCursorImpl::LoadCurrentRow() {
+  const char* key_position = iterator_->Key().begin();
+  const char* key_limit = iterator_->Key().end();
+
+  ObjectStoreDataKey object_store_data_key;
+  key_position = ObjectStoreDataKey::Decode(
+      key_position, key_limit, &object_store_data_key);
+  if (!key_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  current_key_ = object_store_data_key.user_key();
+
+  int64_t version;
+  const char* value_position = DecodeVarInt(
+      iterator_->Value().begin(), iterator_->Value().end(), version);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  // TODO: This re-encodes what was just decoded; try and optimize.
+  record_identifier_.Reset(EncodeIDBKey(*current_key_), version);
+
+  return true;
+}
+
+class ObjectStoreCursorImpl : public IndexedDBBackingStore::Cursor {
+ public:
+  ObjectStoreCursorImpl(
+      LevelDBTransaction* transaction,
+      const IndexedDBBackingStore::Cursor::CursorOptions& cursor_options)
+      : IndexedDBBackingStore::Cursor(transaction, cursor_options) {}
+
+  virtual Cursor* Clone() OVERRIDE { return new ObjectStoreCursorImpl(this); }
+
+  // IndexedDBBackingStore::Cursor
+  virtual std::vector<char>* Value() OVERRIDE { return &current_value_; }
+  virtual bool LoadCurrentRow() OVERRIDE;
+
+ protected:
+  virtual std::vector<char> EncodeKey(const IndexedDBKey& key) OVERRIDE {
+    return ObjectStoreDataKey::Encode(
+        cursor_options_.database_id, cursor_options_.object_store_id, key);
+  }
+
+ private:
+  explicit ObjectStoreCursorImpl(const ObjectStoreCursorImpl* other)
+      : IndexedDBBackingStore::Cursor(other),
+        current_value_(other->current_value_) {}
+
+  std::vector<char> current_value_;
+};
+
+bool ObjectStoreCursorImpl::LoadCurrentRow() {
+  const char* key_position = iterator_->Key().begin();
+  const char* key_limit = iterator_->Key().end();
+
+  ObjectStoreDataKey object_store_data_key;
+  key_position = ObjectStoreDataKey::Decode(
+      key_position, key_limit, &object_store_data_key);
+  if (!key_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  current_key_ = object_store_data_key.user_key();
+
+  int64_t version;
+  const char* value_position = DecodeVarInt(
+      iterator_->Value().begin(), iterator_->Value().end(), version);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  // TODO: This re-encodes what was just decoded; try and optimize.
+  record_identifier_.Reset(EncodeIDBKey(*current_key_), version);
+
+  std::vector<char> value;
+  value.insert(value.end(), value_position, iterator_->Value().end());
+  current_value_.swap(value);
+  return true;
+}
+
+class IndexKeyCursorImpl : public IndexedDBBackingStore::Cursor {
+ public:
+  IndexKeyCursorImpl(
+      LevelDBTransaction* transaction,
+      const IndexedDBBackingStore::Cursor::CursorOptions& cursor_options)
+      : IndexedDBBackingStore::Cursor(transaction, cursor_options) {}
+
+  virtual Cursor* Clone() OVERRIDE { return new IndexKeyCursorImpl(this); }
+
+  // IndexedDBBackingStore::Cursor
+  virtual std::vector<char>* Value() OVERRIDE {
+    NOTREACHED();
+    return NULL;
+  }
+  virtual const IndexedDBKey& primary_key() const OVERRIDE {
+    return *primary_key_;
+  }
+  virtual const IndexedDBBackingStore::RecordIdentifier&
+  RecordIdentifier() const {
+    NOTREACHED();
+    return record_identifier_;
+  }
+  virtual bool LoadCurrentRow() OVERRIDE;
+
+ protected:
+  virtual std::vector<char> EncodeKey(const IndexedDBKey& key) OVERRIDE {
+    return IndexDataKey::Encode(cursor_options_.database_id,
+                                cursor_options_.object_store_id,
+                                cursor_options_.index_id,
+                                key);
+  }
+
+ private:
+  explicit IndexKeyCursorImpl(const IndexKeyCursorImpl* other)
+      : IndexedDBBackingStore::Cursor(other),
+        primary_key_(other->primary_key_.get()) {}
+
+  scoped_ptr<IndexedDBKey> primary_key_;
+};
+
+bool IndexKeyCursorImpl::LoadCurrentRow() {
+  const char* key_position = iterator_->Key().begin();
+  const char* key_limit = iterator_->Key().end();
+
+  IndexDataKey index_data_key;
+  key_position = IndexDataKey::Decode(key_position, key_limit, &index_data_key);
+
+  current_key_ = index_data_key.user_key();
+  DCHECK(current_key_);
+
+  int64_t index_data_version;
+  const char* value_position = DecodeVarInt(
+      iterator_->Value().begin(), iterator_->Value().end(), index_data_version);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  value_position =
+      DecodeIDBKey(value_position, iterator_->Value().end(), &primary_key_);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  std::vector<char> primary_leveldb_key =
+      ObjectStoreDataKey::Encode(index_data_key.DatabaseId(),
+                                 index_data_key.ObjectStoreId(),
+                                 *primary_key_);
+
+  std::vector<char> result;
+  bool found = false;
+  bool ok = transaction_->Get(LevelDBSlice(primary_leveldb_key), result, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+  if (!found) {
+    transaction_->Remove(iterator_->Key());
+    return false;
+  }
+
+  int64_t object_store_data_version;
+  const char* t =
+      DecodeVarInt(&*result.begin(), &*result.end(), object_store_data_version);
+  if (!t) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  if (object_store_data_version != index_data_version) {
+    transaction_->Remove(iterator_->Key());
+    return false;
+  }
+
+  return true;
+}
+
+class IndexCursorImpl : public IndexedDBBackingStore::Cursor {
+ public:
+  IndexCursorImpl(
+      LevelDBTransaction* transaction,
+      const IndexedDBBackingStore::Cursor::CursorOptions& cursor_options)
+      : IndexedDBBackingStore::Cursor(transaction, cursor_options) {}
+
+  virtual Cursor* Clone() OVERRIDE { return new IndexCursorImpl(this); }
+
+  // IndexedDBBackingStore::Cursor
+  virtual std::vector<char>* Value() OVERRIDE { return &current_value_; }
+  virtual const IndexedDBKey& primary_key() const OVERRIDE {
+    return *primary_key_;
+  }
+  virtual const IndexedDBBackingStore::RecordIdentifier&
+  RecordIdentifier() const {
+    NOTREACHED();
+    return record_identifier_;
+  }
+  virtual bool LoadCurrentRow() OVERRIDE;
+
+ protected:
+  virtual std::vector<char> EncodeKey(const IndexedDBKey& key) OVERRIDE {
+    return IndexDataKey::Encode(cursor_options_.database_id,
+                                cursor_options_.object_store_id,
+                                cursor_options_.index_id,
+                                key);
+  }
+
+ private:
+  explicit IndexCursorImpl(const IndexCursorImpl* other)
+      : IndexedDBBackingStore::Cursor(other),
+        primary_key_(other->primary_key_.get()),
+        current_value_(other->current_value_),
+        primary_leveldb_key_(other->primary_leveldb_key_) {}
+
+  scoped_ptr<IndexedDBKey> primary_key_;
+  std::vector<char> current_value_;
+  std::vector<char> primary_leveldb_key_;
+};
+
+bool IndexCursorImpl::LoadCurrentRow() {
+  const char* key_position = iterator_->Key().begin();
+  const char* key_limit = iterator_->Key().end();
+
+  IndexDataKey index_data_key;
+  key_position = IndexDataKey::Decode(key_position, key_limit, &index_data_key);
+
+  current_key_ = index_data_key.user_key();
+  DCHECK(current_key_);
+
+  const char* value_position = iterator_->Value().begin();
+  const char* value_limit = iterator_->Value().end();
+
+  int64_t index_data_version;
+  value_position =
+      DecodeVarInt(value_position, value_limit, index_data_version);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+  value_position = DecodeIDBKey(value_position, value_limit, &primary_key_);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  primary_leveldb_key_ =
+      ObjectStoreDataKey::Encode(index_data_key.DatabaseId(),
+                                 index_data_key.ObjectStoreId(),
+                                 *primary_key_);
+
+  std::vector<char> result;
+  bool found = false;
+  bool ok =
+      transaction_->Get(LevelDBSlice(primary_leveldb_key_), result, found);
+  if (!ok) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+  if (!found) {
+    transaction_->Remove(iterator_->Key());
+    return false;
+  }
+
+  int64_t object_store_data_version;
+  value_position =
+      DecodeVarInt(&*result.begin(), &*result.end(), object_store_data_version);
+  if (!value_position) {
+    INTERNAL_READ_ERROR(kLoadCurrentRow);
+    return false;
+  }
+
+  if (object_store_data_version != index_data_version) {
+    transaction_->Remove(iterator_->Key());
+    return false;
+  }
+
+  // TODO: Make value_position an iterator.
+  std::vector<char> value(std::vector<char>::const_iterator(value_position),
+                          std::vector<char>::const_iterator(result.end()));
+  current_value_.swap(value);
+  return true;
+}
+
+bool ObjectStoreCursorOptions(
+    LevelDBTransaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const IndexedDBKeyRange& range,
+    IndexedDB::CursorDirection direction,
+    IndexedDBBackingStore::Cursor::CursorOptions& cursor_options) {
+  cursor_options.database_id = database_id;
+  cursor_options.object_store_id = object_store_id;
+
+  bool lower_bound = range.lower().IsValid();
+  bool upper_bound = range.upper().IsValid();
+  cursor_options.forward = (direction == IndexedDB::CursorNextNoDuplicate ||
+                            direction == IndexedDB::CursorNext);
+  cursor_options.unique = (direction == IndexedDB::CursorNextNoDuplicate ||
+                           direction == IndexedDB::CursorPrevNoDuplicate);
+
+  if (!lower_bound) {
+    cursor_options.low_key =
+        ObjectStoreDataKey::Encode(database_id, object_store_id, MinIDBKey());
+    cursor_options.low_open = true;  // Not included.
+  } else {
+    cursor_options.low_key =
+        ObjectStoreDataKey::Encode(database_id, object_store_id, range.lower());
+    cursor_options.low_open = range.lowerOpen();
+  }
+
+  if (!upper_bound) {
+    cursor_options.high_key =
+        ObjectStoreDataKey::Encode(database_id, object_store_id, MaxIDBKey());
+
+    if (cursor_options.forward) {
+      cursor_options.high_open = true;  // Not included.
+    } else {
+      // We need a key that exists.
+      if (!FindGreatestKeyLessThanOrEqual(
+              transaction, cursor_options.high_key, cursor_options.high_key))
+        return false;
+      cursor_options.high_open = false;
+    }
+  } else {
+    cursor_options.high_key =
+        ObjectStoreDataKey::Encode(database_id, object_store_id, range.upper());
+    cursor_options.high_open = range.upperOpen();
+
+    if (!cursor_options.forward) {
+      // For reverse cursors, we need a key that exists.
+      std::vector<char> found_high_key;
+      if (!FindGreatestKeyLessThanOrEqual(
+              transaction, cursor_options.high_key, found_high_key))
+        return false;
+
+      // If the target key should not be included, but we end up with a smaller
+      // key, we should include that.
+      if (cursor_options.high_open &&
+          CompareIndexKeys(LevelDBSlice(found_high_key),
+                           LevelDBSlice(cursor_options.high_key)) <
+              0)
+        cursor_options.high_open = false;
+
+      cursor_options.high_key = found_high_key;
+    }
+  }
+
+  return true;
+}
+
+bool IndexCursorOptions(
+    LevelDBTransaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKeyRange& range,
+    IndexedDB::CursorDirection direction,
+    IndexedDBBackingStore::Cursor::CursorOptions& cursor_options) {
+  DCHECK(transaction);
+  if (!KeyPrefix::ValidIds(database_id, object_store_id, index_id))
+    return false;
+
+  cursor_options.database_id = database_id;
+  cursor_options.object_store_id = object_store_id;
+  cursor_options.index_id = index_id;
+
+  bool lower_bound = range.lower().IsValid();
+  bool upper_bound = range.upper().IsValid();
+  cursor_options.forward = (direction == IndexedDB::CursorNextNoDuplicate ||
+                            direction == IndexedDB::CursorNext);
+  cursor_options.unique = (direction == IndexedDB::CursorNextNoDuplicate ||
+                           direction == IndexedDB::CursorPrevNoDuplicate);
+
+  if (!lower_bound) {
+    cursor_options.low_key =
+        IndexDataKey::EncodeMinKey(database_id, object_store_id, index_id);
+    cursor_options.low_open = false;  // Included.
+  } else {
+    cursor_options.low_key = IndexDataKey::Encode(
+        database_id, object_store_id, index_id, range.lower());
+    cursor_options.low_open = range.lowerOpen();
+  }
+
+  if (!upper_bound) {
+    cursor_options.high_key =
+        IndexDataKey::EncodeMaxKey(database_id, object_store_id, index_id);
+    cursor_options.high_open = false;  // Included.
+
+    if (!cursor_options.forward) {  // We need a key that exists.
+      if (!FindGreatestKeyLessThanOrEqual(
+              transaction, cursor_options.high_key, cursor_options.high_key))
+        return false;
+      cursor_options.high_open = false;
+    }
+  } else {
+    cursor_options.high_key = IndexDataKey::Encode(
+        database_id, object_store_id, index_id, range.upper());
+    cursor_options.high_open = range.upperOpen();
+
+    std::vector<char> found_high_key;
+    if (!FindGreatestKeyLessThanOrEqual(
+            transaction,
+            cursor_options.high_key,
+            found_high_key))  // Seek to the *last* key in the set of non-unique
+                              // keys.
+      return false;
+
+    // If the target key should not be included, but we end up with a smaller
+    // key, we should include that.
+    if (cursor_options.high_open &&
+        CompareIndexKeys(LevelDBSlice(found_high_key),
+                         LevelDBSlice(cursor_options.high_key)) <
+            0)
+      cursor_options.high_open = false;
+
+    cursor_options.high_key = found_high_key;
+  }
+
+  return true;
+}
+
+scoped_ptr<IndexedDBBackingStore::Cursor>
+IndexedDBBackingStore::OpenObjectStoreCursor(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const IndexedDBKeyRange& range,
+    IndexedDB::CursorDirection direction) {
+  IDB_TRACE("IndexedDBBackingStore::open_object_store_cursor");
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  IndexedDBBackingStore::Cursor::CursorOptions cursor_options;
+  if (!ObjectStoreCursorOptions(leveldb_transaction,
+                                database_id,
+                                object_store_id,
+                                range,
+                                direction,
+                                cursor_options))
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+  scoped_ptr<ObjectStoreCursorImpl> cursor(
+      new ObjectStoreCursorImpl(leveldb_transaction, cursor_options));
+  if (!cursor->FirstSeek())
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+
+  return cursor.PassAs<IndexedDBBackingStore::Cursor>();
+}
+
+scoped_ptr<IndexedDBBackingStore::Cursor>
+IndexedDBBackingStore::OpenObjectStoreKeyCursor(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    const IndexedDBKeyRange& range,
+    IndexedDB::CursorDirection direction) {
+  IDB_TRACE("IndexedDBBackingStore::open_object_store_key_cursor");
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  IndexedDBBackingStore::Cursor::CursorOptions cursor_options;
+  if (!ObjectStoreCursorOptions(leveldb_transaction,
+                                database_id,
+                                object_store_id,
+                                range,
+                                direction,
+                                cursor_options))
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+  scoped_ptr<ObjectStoreKeyCursorImpl> cursor(
+      new ObjectStoreKeyCursorImpl(leveldb_transaction, cursor_options));
+  if (!cursor->FirstSeek())
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+
+  return cursor.PassAs<IndexedDBBackingStore::Cursor>();
+}
+
+scoped_ptr<IndexedDBBackingStore::Cursor>
+IndexedDBBackingStore::OpenIndexKeyCursor(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKeyRange& range,
+    IndexedDB::CursorDirection direction) {
+  IDB_TRACE("IndexedDBBackingStore::open_index_key_cursor");
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  IndexedDBBackingStore::Cursor::CursorOptions cursor_options;
+  if (!IndexCursorOptions(leveldb_transaction,
+                          database_id,
+                          object_store_id,
+                          index_id,
+                          range,
+                          direction,
+                          cursor_options))
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+  scoped_ptr<IndexKeyCursorImpl> cursor(
+      new IndexKeyCursorImpl(leveldb_transaction, cursor_options));
+  if (!cursor->FirstSeek())
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+
+  return cursor.PassAs<IndexedDBBackingStore::Cursor>();
+}
+
+scoped_ptr<IndexedDBBackingStore::Cursor>
+IndexedDBBackingStore::OpenIndexCursor(
+    IndexedDBBackingStore::Transaction* transaction,
+    int64_t database_id,
+    int64_t object_store_id,
+    int64_t index_id,
+    const IndexedDBKeyRange& range,
+    IndexedDB::CursorDirection direction) {
+  IDB_TRACE("IndexedDBBackingStore::open_index_cursor");
+  LevelDBTransaction* leveldb_transaction =
+      IndexedDBBackingStore::Transaction::LevelDBTransactionFrom(transaction);
+  IndexedDBBackingStore::Cursor::CursorOptions cursor_options;
+  if (!IndexCursorOptions(leveldb_transaction,
+                          database_id,
+                          object_store_id,
+                          index_id,
+                          range,
+                          direction,
+                          cursor_options))
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+  scoped_ptr<IndexCursorImpl> cursor(
+      new IndexCursorImpl(leveldb_transaction, cursor_options));
+  if (!cursor->FirstSeek())
+    return scoped_ptr<IndexedDBBackingStore::Cursor>();
+
+  return cursor.PassAs<IndexedDBBackingStore::Cursor>();
+}
+
+IndexedDBBackingStore::Transaction::Transaction(
+    IndexedDBBackingStore* backing_store)
+    : backing_store_(backing_store) {}
+
+IndexedDBBackingStore::Transaction::~Transaction() {}
+
+void IndexedDBBackingStore::Transaction::begin() {
+  IDB_TRACE("IndexedDBBackingStore::Transaction::begin");
+  DCHECK(!transaction_);
+  transaction_ = LevelDBTransaction::Create(backing_store_->db_.get());
+}
+
+bool IndexedDBBackingStore::Transaction::Commit() {
+  IDB_TRACE("IndexedDBBackingStore::Transaction::commit");
+  DCHECK(transaction_);
+  bool result = transaction_->Commit();
+  transaction_ = NULL;
+  if (!result)
+    INTERNAL_WRITE_ERROR(kTransactionCommit);
+  return result;
+}
+
+void IndexedDBBackingStore::Transaction::Rollback() {
+  IDB_TRACE("IndexedDBBackingStore::Transaction::rollback");
+  DCHECK(transaction_);
+  transaction_->Rollback();
+  transaction_ = NULL;
+}
+
+}  // namespace content