Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

chrome/browser/extensions/api/chrome_extensions_api_client.h

Index: chrome/browser/extensions/api/chrome_extensions_api_client.h
diff --git a/chrome/browser/extensions/api/chrome_extensions_api_client.h b/chrome/browser/extensions/api/chrome_extensions_api_client.h
new file mode 100644
index 0000000000000000000000000000000000000000..1ce28270d9a4373728d82cf3c9324fcdf6056b35
--- /dev/null
+++ b/chrome/browser/extensions/api/chrome_extensions_api_client.h
@@ -0,0 +1,33 @@
+// Copyright 2014 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_API_CHROME_EXTENSIONS_API_CLIENT_H_
+#define CHROME_BROWSER_EXTENSIONS_API_CHROME_EXTENSIONS_API_CLIENT_H_
+
+#include "base/compiler_specific.h"
+#include "extensions/browser/api/extensions_api_client.h"
+
+namespace extensions {
+
+// Support for extensions APIs in Chrome.

[Yoyo Zhou, 2014/03/04 19:55:04]

nit: This is more like extra support.

[James Cook, 2014/03/04 20:55:58]

Done.

+class ChromeExtensionsApiClient : public ExtensionsApiClient {
+ public:
+  ChromeExtensionsApiClient();
+  virtual ~ChromeExtensionsApiClient();
+
+  // ExtensionsApiClient implementation.
+  virtual void AddAdditionalValueStoreCaches(
+      content::BrowserContext* context,
+      scoped_refptr<SettingsStorageFactory> factory,
+      scoped_refptr<ObserverListThreadSafe<SettingsObserver> > observers,
+      std::map<settings_namespace::Namespace, ValueStoreCache*>* caches)
+      OVERRIDE;
+
+ private:
+  DISALLOW_COPY_AND_ASSIGN(ChromeExtensionsApiClient);
+};
+
+}  // namespace extensions
+
+#endif  // CHROME_BROWSER_EXTENSIONS_API_CHROME_EXTENSIONS_API_CLIENT_H_