Push API: define push event on Service Worker.

public/web/WebServiceWorkerContextProxy.h

 /*
  * Copyright (C) 2013 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 36 matching lines @@
     // FIXME: This needs to pass the active service worker info.
     virtual void dispatchInstallEvent(int installEventID) = 0;
     // FIXME: This needs to pass the fetch request info.
     virtual void dispatchFetchEvent(int fetchEventID) = 0;
 
     virtual void dispatchMessageEvent(const WebString& message, const WebMessagePortChannelArray& channels) = 0;
 
     // Once the ServiceWorker has finished handling the sync event
     // didHandleSyncEvent is called on the context client.
     virtual void dispatchSyncEvent(int syncEventID) = 0;
+
+    // Once the ServiceWorker has finished handling the push event
+    // didHandlePushEvent is called on the context client.
+    virtual void dispatchPushEvent(int eventID, const WebString& data) = 0;
 };
 
 } // namespace blink
 
 #endif // WebServiceWorkerContextProxy_h