Start to implement FetchEvent for ServiceWorker

public/web/WebServiceWorkerContextClient.h

Index: public/web/WebServiceWorkerContextClient.h
diff --git a/public/web/WebServiceWorkerContextClient.h b/public/web/WebServiceWorkerContextClient.h
index 5ab7a3881dbf3788449d840796f630f66d372564..6c1bcd3fa5442915bc16f8a400ce31f58d1afa0c 100644
--- a/public/web/WebServiceWorkerContextClient.h
+++ b/public/web/WebServiceWorkerContextClient.h
@@ -37,6 +37,7 @@ namespace blink {
 
 class WebString;
 class WebServiceWorkerContextProxy;
+struct WebServiceWorkerFetchResponse;
 
 // This interface is implemented by the client. It is suppoed to be created
 // on the main thread and then passed on to the worker thread to be owned
@@ -77,6 +78,10 @@ public:
     // via WebServiceWorkerContextProxy) is handled by the ServiceWorker's
     // script context.
     virtual void didHandleInstallEvent(int installEventID) { }
+
+    // ServiceWorker specific method. Called after FetchEvent is handled by the
+    // ServiceWorker's script context.
+    virtual void didHandleFetchEvent(int fetchEventID, const WebServiceWorkerFetchResponse& response) { }
 };
 
 } // namespace blink