ServiceWorker: Add prepare_callback in DispatchFetchEvent to notify the end of SW preparation.

content/browser/service_worker/service_worker_fetch_dispatcher.h

Index: content/browser/service_worker/service_worker_fetch_dispatcher.h
diff --git a/content/browser/service_worker/service_worker_fetch_dispatcher.h b/content/browser/service_worker/service_worker_fetch_dispatcher.h
index 7b905e0b35d7fe5cc78d473f70b9dbad4d5d4cdd..f20fb9495487bb3d38723c953c9811c9fe21c6e5 100644
--- a/content/browser/service_worker/service_worker_fetch_dispatcher.h
+++ b/content/browser/service_worker/service_worker_fetch_dispatcher.h
@@ -24,7 +24,8 @@ class ServiceWorkerFetchDispatcher {
 
   ServiceWorkerFetchDispatcher(scoped_ptr<ServiceWorkerFetchRequest> request,
                                ServiceWorkerVersion* version,
-                               const FetchCallback& callback);
+                               const base::Closure& prepare_callback,
+                               const FetchCallback& fetch_callback);
   ~ServiceWorkerFetchDispatcher();
 
   // Dispatches a fetch event to the |version| given in ctor, and fires
@@ -35,12 +36,14 @@ class ServiceWorkerFetchDispatcher {
   void DidWaitActivation();
   void DidFailActivation();
   void DispatchFetchEvent();
+  void DidPrepare();
   void DidFinish(ServiceWorkerStatusCode status,
                  ServiceWorkerFetchEventResult fetch_result,
                  const ServiceWorkerResponse& response);
 
   scoped_refptr<ServiceWorkerVersion> version_;
-  FetchCallback callback_;
+  base::Closure prepare_callback_;
+  FetchCallback fetch_callback_;
   scoped_ptr<ServiceWorkerFetchRequest> request_;
   base::WeakPtrFactory<ServiceWorkerFetchDispatcher> weak_factory_;