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

chrome/browser/extensions/settings/syncable_settings_storage.h

-// 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.
 
 #ifndef CHROME_BROWSER_EXTENSIONS_SETTINGS_SYNCABLE_SETTINGS_STORAGE_H_
 #define CHROME_BROWSER_EXTENSIONS_SETTINGS_SYNCABLE_SETTINGS_STORAGE_H_
 #pragma once
 
 #include "base/compiler_specific.h"
 #include "base/memory/weak_ptr.h"
 #include "base/observer_list_threadsafe.h"
@@ skipping 12 matching lines @@
   explicit SyncableSettingsStorage(
       const scoped_refptr<ObserverListThreadSafe<SettingsObserver> >&
           observers,
       const std::string& extension_id,
       // Ownership taken.
       SettingsStorage* delegate);
 
   virtual ~SyncableSettingsStorage();
 
   // SettingsStorage implementation.
+  virtual size_t GetBytesInUse(const std::string& key) OVERRIDE;
+  virtual size_t GetBytesInUse(const std::vector<std::string>& keys) OVERRIDE;
+  virtual size_t GetBytesInUse() OVERRIDE;
   virtual ReadResult Get(const std::string& key) OVERRIDE;
   virtual ReadResult Get(const std::vector<std::string>& keys) OVERRIDE;
   virtual ReadResult Get() OVERRIDE;
   virtual WriteResult Set(
       WriteOptions options,
       const std::string& key,
       const Value& value) OVERRIDE;
   virtual WriteResult Set(
       WriteOptions options, const DictionaryValue& values) OVERRIDE;
   virtual WriteResult Remove(const std::string& key) OVERRIDE;
@@ skipping 69 matching lines @@
   // Keys of the settings that are currently being synced.  Only used to decide
   // whether an ACTION_ADD or ACTION_UPDATE should be sent to sync on a Set().
   std::set<std::string> synced_keys_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncableSettingsStorage);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_SETTINGS_SYNCABLE_SETTINGS_STORAGE_H_