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

Source/modules/serviceworkers/HeaderMapForEachCallback.idl

Index: Source/modules/serviceworkers/HeaderMapForEachCallback.idl
diff --git a/Source/modules/serviceworkers/HeaderMapForEachCallback.idl b/Source/modules/serviceworkers/HeaderMapForEachCallback.idl
deleted file mode 100644
index d6bbb8dfc96e0e4a3c1753d2b6bf38e427baea15..0000000000000000000000000000000000000000
--- a/Source/modules/serviceworkers/HeaderMapForEachCallback.idl
+++ /dev/null
@@ -1,8 +0,0 @@
-// Copyright 2014 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-callback interface HeaderMapForEachCallback {
-    [CallWith=ThisValue] boolean handleItem(DOMString value, DOMString key, HeaderMap map);
-    boolean handleItem(DOMString value, DOMString key, HeaderMap map);
-};