[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 eadbc97ca2ff94c562512a878e4cf1c3058ce861..7dc3f2533dacfc6fde64c7efb7ec942f23d2dec2 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;