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

chrome/browser/shell_integration.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_SHELL_INTEGRATION_H_
 #define CHROME_BROWSER_SHELL_INTEGRATION_H_
 #pragma once
 
 #include <string>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/string16.h"
 #include "googleurl/src/gurl.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 
 class CommandLine;
 class FilePath;
-class PrefService;
 
 #if defined(USE_X11)
 namespace base {
 class Environment;
 }
 #endif
 
 class ShellIntegration {
  public:
   // Sets Chrome as the default browser (only for the current user). Returns
@@ skipping 242 matching lines @@
     // Set Chrome as the default handler for this protocol.
     virtual void SetAsDefault();
 
     std::string protocol_;
 
     DISALLOW_COPY_AND_ASSIGN(DefaultProtocolClientWorker);
   };
 };
 
 #endif  // CHROME_BROWSER_SHELL_INTEGRATION_H_