Extension Storage API: expose storage quota information to extensions, via:

chrome/browser/extensions/settings/settings_leveldb_storage.cc

-// Copyright (c) 2011 The Chromium Authors. All rights reserved.
+// Copyright (c) 2012 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 "chrome/browser/extensions/settings/settings_leveldb_storage.h"
 
 #include "base/bind.h"
 #include "base/compiler_specific.h"
 #include "base/file_util.h"
 #include "base/json/json_reader.h"
 #include "base/json/json_writer.h"
@@ skipping 76 matching lines @@
   if (IsEmpty()) {
     // Close |db_| now to release any lock on the directory.
     db_.reset();
     if (!file_util::Delete(db_path_, true)) {
       LOG(WARNING) << "Failed to delete extension settings directory " <<
           db_path_.value();
     }
   }
 }
 
+size_t SettingsLeveldbStorage::GetBytesInUse(const std::string& key) {
+  // Let SettingsStorageQuotaEnforcer implement this.
+  NOTREACHED() << "Not implemented";
+  return 0;
+}
+
+size_t SettingsLeveldbStorage::GetBytesInUse(
+    const std::vector<std::string>& keys) {
+  // Let SettingsStorageQuotaEnforcer implement this.
+  NOTREACHED() << "Not implemented";
+  return 0;
+}
+
+size_t SettingsLeveldbStorage::GetBytesInUse() {
+  // Let SettingsStorageQuotaEnforcer implement this.
+  NOTREACHED() << "Not implemented";
+  return 0;
+}
+
 SettingsStorage::ReadResult SettingsLeveldbStorage::Get(
     const std::string& key) {
   DCHECK(BrowserThread::CurrentlyOn(BrowserThread::FILE));
   scoped_ptr<Value> setting;
   if (!ReadFromDb(leveldb::ReadOptions(), key, &setting)) {
     return ReadResult(kGenericOnFailureMessage);
   }
   DictionaryValue* settings = new DictionaryValue();
   if (setting.get()) {
     settings->SetWithoutPathExpansion(key, setting.release());
@@ skipping 210 matching lines @@
   it->SeekToFirst();
   bool is_empty = !it->Valid();
   if (!it->status().ok()) {
     LOG(ERROR) << "Checking DB emptiness failed: " << it->status().ToString();
     return false;
   }
   return is_empty;
 }
 
 }  // namespace extensions