Update HTTPHeaderMap wrappers to use AtomicString type for header values

Source/core/loader/FrameLoader.h

 /*
  * Copyright (C) 2006, 2007, 2008, 2009, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) Research In Motion Limited 2009. All rights reserved.
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
@@ skipping 128 matching lines @@
     CachePolicy subresourceCachePolicy() const;
 
     void didFirstLayout();
 
     void checkLoadComplete(DocumentLoader*);
     void checkLoadComplete();
     void detachFromParent();
 
     void addExtraFieldsToRequest(ResourceRequest&);
 
-    static void addHTTPOriginIfNeeded(ResourceRequest&, const String& origin);
+    static void addHTTPOriginIfNeeded(ResourceRequest&, const AtomicString& origin);
 
     FrameLoaderClient* client() const { return m_client; }
 
     void setDefersLoading(bool);
 
     void didExplicitOpen();
 
     // Callbacks from DocumentWriter
     void didBeginDocument(bool dispatchWindowObjectAvailable);
 
@@ skipping 128 matching lines @@
 
     bool m_didAccessInitialDocument;
     Timer<FrameLoader> m_didAccessInitialDocumentTimer;
 
     SandboxFlags m_forcedSandboxFlags;
 };
 
 } // namespace WebCore
 
 #endif // FrameLoader_h