ServiceWorker: Introduce ExtendableMessageEvent to replace MessageEvent

public/web/WebServiceWorkerContextProxy.h

Index: public/web/WebServiceWorkerContextProxy.h
diff --git a/public/web/WebServiceWorkerContextProxy.h b/public/web/WebServiceWorkerContextProxy.h
index ec71310cedf5532c6a87e84cbb6459c4626d0c09..99e2313dd335d9995feba4360d9714d8a622893b 100644
--- a/public/web/WebServiceWorkerContextProxy.h
+++ b/public/web/WebServiceWorkerContextProxy.h
@@ -39,6 +39,8 @@ namespace blink {
 struct WebCircularGeofencingRegion;
 struct WebCrossOriginServiceWorkerClient;
 struct WebNotificationData;
+struct WebServiceWorkerClientInfo;
+class WebServiceWorker;
 class WebServiceWorkerRegistration;
 class WebServiceWorkerRequest;
 class WebString;
@@ -57,7 +59,9 @@ public:
 
     virtual void dispatchGeofencingEvent(int eventID, WebGeofencingEventType, const WebString& regionID, const WebCircularGeofencingRegion&) = 0;
 
-    virtual void dispatchMessageEvent(const WebString& message, const WebMessagePortChannelArray& channels) = 0;
+    virtual void dispatchMessageEvent(int eventID, const WebServiceWorkerClientInfo&, const WebString& message, const WebMessagePortChannelArray& channels) = 0;
+
+    virtual void dispatchMessageEvent(int eventID, WebServiceWorker*, const WebString& message, const WebMessagePortChannelArray& channels) = 0;
 
     virtual void dispatchNotificationClickEvent(int eventID, int64_t notificationID, const WebNotificationData&) = 0;