Cleanup: Remove forward declarations in various chrome/browser directories.

chrome/browser/prerender/prerender_render_view_host_observer.h

 // Copyright (c) 2011 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 CHROME_BROWSER_PRERENDER_PRERENDER_RENDER_VIEW_HOST_OBSERVER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_RENDER_VIEW_HOST_OBSERVER_H_
 
+#include <vector>
+
 #include "content/browser/renderer_host/render_view_host_observer.h"
 
-#include <string>
-#include <vector>
-
 struct FaviconURL;
-class GURL;
 class RenderViewHost;
 
 namespace IPC {
 class Message;
 }
 
 namespace prerender {
 
 class PrerenderContents;
 
@@ skipping 15 matching lines @@
  private:
   // Message handlers.
   void OnUpdateFaviconURL(int32 page_id, const std::vector<FaviconURL>& urls);
   void OnMaybeCancelPrerenderForHTML5Media();
   void OnCancelPrerenderForPrinting();
 
   // The associated prerender contents.
   PrerenderContents* prerender_contents_;
 };
 
-}
+}  // namespace prerender
+
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_RENDER_VIEW_HOST_OBSERVER_H_