Add IDL and initial Blink API for Background Sync

public/platform/Platform.h

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 83 matching lines @@
 class WebRTCPeerConnectionHandler;
 class WebRTCPeerConnectionHandlerClient;
 class WebSandboxSupport;
 class WebScheduler;
 class WebSecurityOrigin;
 class WebScrollbarBehavior;
 class WebSocketHandle;
 class WebSpeechSynthesizer;
 class WebSpeechSynthesizerClient;
 class WebStorageNamespace;
+class WebSyncProvider;
 struct WebFloatPoint;
 class WebThemeEngine;
 class WebThread;
 class WebURL;
 class WebURLLoader;
 class WebUnitTestSupport;
 class WebWaitableEvent;
 struct WebLocalizedString;
 struct WebSize;
 
@@ skipping 545 matching lines @@
 
     // navigator.connect --------------------------------------------------
 
     virtual WebNavigatorConnectProvider* navigatorConnectProvider() { return 0; }
 
     // Permissions --------------------------------------------------------
 
     virtual WebPermissionClient* permissionClient() { return 0; }
 
 
+    // Background Sync API------------------------------------------------------------
+
+    virtual WebSyncProvider* backgroundSyncProvider() { return 0; }
+
 protected:
     BLINK_PLATFORM_EXPORT Platform();
     virtual ~Platform() { }
 
     WebThread* m_mainThread;
 };
 
 } // namespace blink
 
 #endif