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

chrome/browser/extensions/settings/failing_settings_storage.h

Index: chrome/browser/extensions/settings/failing_settings_storage.h
diff --git a/chrome/browser/extensions/settings/failing_settings_storage.h b/chrome/browser/extensions/settings/failing_settings_storage.h
index ad97cfc4d9f794e6f81232859bc5e511967f5ef7..e99b7ea68fbdb2f03b601f3f226cefc38ee5b860 100644
--- a/chrome/browser/extensions/settings/failing_settings_storage.h
+++ b/chrome/browser/extensions/settings/failing_settings_storage.h
@@ -1,4 +1,4 @@
-// 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.
 
@@ -17,6 +17,9 @@ class FailingSettingsStorage : public SettingsStorage {
   FailingSettingsStorage() {}
 
   // 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;