Add ExtensionsApiClient interface, use it in the storage API SettingsFrontend

apps/shell/browser/shell_extensions_browser_client.h

 // Copyright 2013 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 APPS_SHELL_BROWSER_SHELL_EXTENSIONS_BROWSER_CLIENT_H_
 #define APPS_SHELL_BROWSER_SHELL_EXTENSIONS_BROWSER_CLIENT_H_
 
 #include "base/compiler_specific.h"
 #include "extensions/browser/extensions_browser_client.h"
 
 class PrefService;
 
 namespace extensions {
 
+class ExtensionsApiClient;
+
 // An ExtensionsBrowserClient that supports a single content::BrowserContent
 // with no related incognito context.
 class ShellExtensionsBrowserClient : public ExtensionsBrowserClient {
  public:
   // |context| is the single BrowserContext used for IsValidContext() below.
   explicit ShellExtensionsBrowserClient(content::BrowserContext* context);
   virtual ~ShellExtensionsBrowserClient();
 
   // ExtensionsBrowserClient overrides:
   virtual bool IsShuttingDown() OVERRIDE;
@@ skipping 31 matching lines @@
   virtual content::JavaScriptDialogManager* GetJavaScriptDialogManager()
       OVERRIDE;
   virtual ApiActivityMonitor* GetApiActivityMonitor(
       content::BrowserContext* context) OVERRIDE;
   virtual ExtensionSystemProvider* GetExtensionSystemFactory() OVERRIDE;
 
  private:
   // The single BrowserContext for app_shell. Not owned.
   content::BrowserContext* browser_context_;
 
+  // Support for extension APIs.
+  scoped_ptr<ExtensionsApiClient> api_client_;
+
   // The PrefService for |browser_context_|.
   scoped_ptr<PrefService> prefs_;
 
   DISALLOW_COPY_AND_ASSIGN(ShellExtensionsBrowserClient);
 };
 
 }  // namespace extensions
 
 #endif  // APPS_SHELL_BROWSER_SHELL_EXTENSIONS_BROWSER_CLIENT_H_