[ServiceWorker] Make Request class better conformance with the spec.

Source/modules/serviceworkers/FetchManager.h

Index: Source/modules/serviceworkers/FetchManager.h
diff --git a/Source/modules/serviceworkers/FetchManager.h b/Source/modules/serviceworkers/FetchManager.h
index 730a9a6261be752539a5bc444b9cd31523a8d571..bfdfa7df6e8f07e3c95df6db4c0cc00cd13a4ed5 100644
--- a/Source/modules/serviceworkers/FetchManager.h
+++ b/Source/modules/serviceworkers/FetchManager.h
@@ -21,6 +21,9 @@ public:
     ~FetchManager();
     ScriptPromise fetch(ScriptState*, PassOwnPtr<ResourceRequest>);
 
+    static bool isSimpleMethod(const String&);
+    static bool isForbiddenMethod(const String&);
+    static bool isUsefulMethod(const String&);
 private:
     class Loader;