Add an Error class for ServiceWorkers

public/platform/WebServiceWorkerProvider.h

Index: public/platform/WebServiceWorkerProvider.h
diff --git a/public/platform/WebServiceWorkerProvider.h b/public/platform/WebServiceWorkerProvider.h
index c7f0dc06fa7d05b8a6a356290cdc677a75f6bb78..65c0445f4d86c72dc91fa94fed8920d5577cfb3b 100644
--- a/public/platform/WebServiceWorkerProvider.h
+++ b/public/platform/WebServiceWorkerProvider.h
@@ -38,10 +38,12 @@ namespace WebKit {
 class WebString;
 class WebURL;
 class WebServiceWorker;
+struct WebServiceWorkerError;
 
 class WebServiceWorkerProvider {
 public:
-    typedef WebCallbacks<WebServiceWorker, WebServiceWorker> WebServiceWorkerCallbacks;
+    // The WebServiceWorker and WebServiceWorkerError ownership are passed to the WebServiceWorkerCallbacks implementation.
+    typedef WebCallbacks<WebServiceWorker, WebServiceWorkerError> WebServiceWorkerCallbacks;
     virtual void registerServiceWorker(const WebURL& pattern, const WebURL& scriptUrl, WebServiceWorkerCallbacks*) { }
 
     virtual void unregisterServiceWorker(const WebURL& pattern, WebServiceWorkerCallbacks*) { }