Use a two-part data format version in IndexedDB metadata.

content/browser/indexed_db/indexed_db_backing_store.h

Index: content/browser/indexed_db/indexed_db_backing_store.h
diff --git a/content/browser/indexed_db/indexed_db_backing_store.h b/content/browser/indexed_db/indexed_db_backing_store.h
index 58d40039670082e368865d0ae7cc8e87e470115b..4a821915af3af00a953f2c5bd6736a1533a4a3d0 100644
--- a/content/browser/indexed_db/indexed_db_backing_store.h
+++ b/content/browser/indexed_db/indexed_db_backing_store.h
@@ -30,6 +30,7 @@
 #include "content/browser/indexed_db/leveldb/leveldb_iterator.h"
 #include "content/browser/indexed_db/leveldb/leveldb_transaction.h"
 #include "content/common/content_export.h"
+#include "content/common/indexed_db/indexed_db_data_format_version.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"
@@ -375,6 +376,9 @@ class CONTENT_EXPORT IndexedDBBackingStore
   };
 
   const url::Origin& origin() const { return origin_; }
+  const IndexedDBDataFormatVersion data_format_version() const {

[dcheng, 2017/04/04 19:59:21]

Nit: no const and return by value, or const and return by ref.

+    return data_format_version_;
+  }
   IndexedDBFactory* factory() const { return indexed_db_factory_; }
   base::SequencedTaskRunner* task_runner() const { return task_runner_.get(); }
   base::OneShotTimer* close_timer() { return &close_timer_; }
@@ -386,6 +390,7 @@ class CONTENT_EXPORT IndexedDBBackingStore
       IndexedDBFactory* indexed_db_factory,
       const url::Origin& origin,
       const base::FilePath& path_base,
+      const IndexedDBDataFormatVersion& data_format_version,
       scoped_refptr<net::URLRequestContextGetter> request_context_getter,
       IndexedDBDataLossInfo* data_loss_info,
       bool* disk_full,
@@ -396,6 +401,7 @@ class CONTENT_EXPORT IndexedDBBackingStore
       IndexedDBFactory* indexed_db_factory,
       const url::Origin& origin,
       const base::FilePath& path_base,
+      const IndexedDBDataFormatVersion& data_format_version,
       scoped_refptr<net::URLRequestContextGetter> request_context_getter,
       IndexedDBDataLossInfo* data_loss_info,
       bool* disk_full,
@@ -405,10 +411,12 @@ class CONTENT_EXPORT IndexedDBBackingStore
       leveldb::Status* status);
   static scoped_refptr<IndexedDBBackingStore> OpenInMemory(
       const url::Origin& origin,
+      const IndexedDBDataFormatVersion& data_format_version,
       base::SequencedTaskRunner* task_runner,
       leveldb::Status* status);
   static scoped_refptr<IndexedDBBackingStore> OpenInMemory(
       const url::Origin& origin,
+      const IndexedDBDataFormatVersion& data_format_version,
       LevelDBFactory* leveldb_factory,
       base::SequencedTaskRunner* task_runner,
       leveldb::Status* status);
@@ -590,6 +598,7 @@ class CONTENT_EXPORT IndexedDBBackingStore
       IndexedDBFactory* indexed_db_factory,
       const url::Origin& origin,
       const base::FilePath& blob_path,
+      const IndexedDBDataFormatVersion& data_format_version,
       scoped_refptr<net::URLRequestContextGetter> request_context_getter,
       std::unique_ptr<LevelDBDatabase> db,
       std::unique_ptr<LevelDBComparator> comparator,
@@ -626,6 +635,7 @@ class CONTENT_EXPORT IndexedDBBackingStore
       IndexedDBFactory* indexed_db_factory,
       const url::Origin& origin,
       const base::FilePath& blob_path,
+      const IndexedDBDataFormatVersion& data_format_version,
       scoped_refptr<net::URLRequestContextGetter> request_context_getter,
       std::unique_ptr<LevelDBDatabase> db,
       std::unique_ptr<LevelDBComparator> comparator,
@@ -667,6 +677,7 @@ class CONTENT_EXPORT IndexedDBBackingStore
   IndexedDBFactory* indexed_db_factory_;
   const url::Origin origin_;
   base::FilePath blob_path_;
+  const IndexedDBDataFormatVersion data_format_version_;
 
   // The origin identifier is a key prefix unique to the origin used in the
   // leveldb backing store to partition data by origin. It is a normalized