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

Source/modules/serviceworkers/FetchHeaderList.h

 // 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.
 
 #ifndef FetchHeaderList_h
 #define FetchHeaderList_h
 
 #include "wtf/OwnPtr.h"
 #include "wtf/PassRefPtr.h"
 #include "wtf/RefCounted.h"
 #include "wtf/Vector.h"
 #include "wtf/text/WTFString.h"
 #include <utility>
 
 namespace WebCore {
 
 // http://fetch.spec.whatwg.org/#terminology-headers
 class FetchHeaderList FINAL : public RefCounted<FetchHeaderList> {
 public:
     typedef std::pair<String, String> Header;
     static PassRefPtr<FetchHeaderList> create();
+    PassRefPtr<FetchHeaderList> createCopy();
 
     ~FetchHeaderList();
     void append(const String&, const String&);
     void set(const String&, const String&);
     // FIXME: Implement parse()
     // FIXME: Implement extractMIMEType()
 
     size_t size() const;
     void remove(const String&);
     bool get(const String&, String&) const;
@@ skipping 10 matching lines @@
     static bool isForbiddenResponseHeaderName(const String&);
 
 private:
     FetchHeaderList();
     Vector<OwnPtr<Header> > m_headerList;
 };
 
 } // namespace WebCore
 
 #endif // FetchHeaderList_h