ServiceWorker: Introduce ServiceWorkerMessageEvent to replace MessageEvent (1/3).

public/platform/WebServiceWorkerProviderClient.h

Index: public/platform/WebServiceWorkerProviderClient.h
diff --git a/public/platform/WebServiceWorkerProviderClient.h b/public/platform/WebServiceWorkerProviderClient.h
index d3b679500191a71681f482f6ea131b1bc114eb88..cff4efa3687ef34c272a13c8b264bd2b8bfc57ef 100644
--- a/public/platform/WebServiceWorkerProviderClient.h
+++ b/public/platform/WebServiceWorkerProviderClient.h
@@ -47,7 +47,12 @@ public:
 
     virtual void setController(WebServiceWorker*, bool shouldNotifyControllerChange) = 0;
 
+    // FIXME: Remove this when Chrome side CL landed.
     virtual void dispatchMessageEvent(const WebString& message, const WebMessagePortChannelArray&) = 0;
+    virtual void dispatchMessageEvent(WebServiceWorker*, const WebString& message, const WebMessagePortChannelArray& channels)
+    {
+        return dispatchMessageEvent(message, channels);
+    }
 };
 
 } // namespace blink