Remove obviously unneeded forward declarations in chrome/browser/[abef]*/*.h.

chrome/browser/extensions/user_script_master.h

Index: chrome/browser/extensions/user_script_master.h
diff --git a/chrome/browser/extensions/user_script_master.h b/chrome/browser/extensions/user_script_master.h
index 9f5948ebbf8903771bc12db92db7deaebf8976d7..7fc8a10781dfe269676fd415bb3d08b93bc95363 100644
--- a/chrome/browser/extensions/user_script_master.h
+++ b/chrome/browser/extensions/user_script_master.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2008 The Chromium Authors. All rights reserved.
+// Copyright (c) 2010 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.
 
@@ -18,7 +18,6 @@ namespace base {
 class StringPiece;
 }
 
-class Extension;
 class Profile;
 
 // Manages a segment of shared memory that contains the user scripts the user