Push API: define push event on Service Worker.

public/web/WebServiceWorkerContextProxy.h

Index: public/web/WebServiceWorkerContextProxy.h
diff --git a/public/web/WebServiceWorkerContextProxy.h b/public/web/WebServiceWorkerContextProxy.h
index fb3c7a8c065ed16505bfa29efab9ba96204b26d1..3c8a59c7fc89a5e5969b23dba3ac5da81f22a153 100644
--- a/public/web/WebServiceWorkerContextProxy.h
+++ b/public/web/WebServiceWorkerContextProxy.h
@@ -54,6 +54,10 @@ public:
     // 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