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

chrome/browser/prerender/prerender_tab_helper.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_TAB_HELPER_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_TAB_HELPER_H_
 
 #include "content/browser/tab_contents/tab_contents_observer.h"
 
 #include "base/time.h"
 
 class TabContentsWrapper;
 class GURL;
 
 namespace prerender {
 
-class PrerenderContents;
 class PrerenderManager;
 
 // PrerenderTabHelper is responsible for recording perceived pageload times
 // to compare PLT's with prerendering enabled and disabled.
 class PrerenderTabHelper : public TabContentsObserver {
  public:
   explicit PrerenderTabHelper(TabContentsWrapper* tab);
   virtual ~PrerenderTabHelper();
 
   // TabContentsObserver implementation.
@@ skipping 52 matching lines @@
 
   // Current URL being loaded.
   GURL url_;
 
   DISALLOW_COPY_AND_ASSIGN(PrerenderTabHelper);
 };
 
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_TAB_HELPER_H_