Start to implement FetchEvent for ServiceWorker

Source/modules/serviceworkers/ServiceWorkerGlobalScopeClient.h

Index: Source/modules/serviceworkers/ServiceWorkerGlobalScopeClient.h
diff --git a/Source/modules/serviceworkers/ServiceWorkerGlobalScopeClient.h b/Source/modules/serviceworkers/ServiceWorkerGlobalScopeClient.h
index 9b8437f3202cdc1d7b3c739613fee6421c792f8e..4b01763f0c3fd90706e5dd6b34bc2665b9cc23cb 100644
--- a/Source/modules/serviceworkers/ServiceWorkerGlobalScopeClient.h
+++ b/Source/modules/serviceworkers/ServiceWorkerGlobalScopeClient.h
@@ -38,6 +38,7 @@
 namespace WebCore {
 
 class ExecutionContext;
+class Response;
 class WorkerClients;
 
 class ServiceWorkerGlobalScopeClient : public Supplement<WorkerClients> {
@@ -46,6 +47,8 @@ public:
     virtual ~ServiceWorkerGlobalScopeClient() { }
 
     virtual void didHandleInstallEvent(int installEventID) = 0;
+    // A null response means no valid response was provided by the service worker, so fallback to native.
+    virtual void didHandleFetchEvent(int fetchEventID, PassRefPtr<Response> = nullptr) = 0;
 
     static const char* supplementName();
     static ServiceWorkerGlobalScopeClient* from(ExecutionContext*);