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

chrome/browser/extensions/extension_devtools_manager.h

Index: chrome/browser/extensions/extension_devtools_manager.h
diff --git a/chrome/browser/extensions/extension_devtools_manager.h b/chrome/browser/extensions/extension_devtools_manager.h
index 39f19bba351b8f2e54a33f1f834c9066ec9fbda0..dc2845613af67fbb253ab531e323bd4db4c28e94 100644
--- a/chrome/browser/extensions/extension_devtools_manager.h
+++ b/chrome/browser/extensions/extension_devtools_manager.h
@@ -1,4 +1,4 @@
-// Copyright (c) 2009 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.
 
@@ -9,6 +9,7 @@
 #include <map>
 #include <set>
 #include <string>
+
 #include "base/linked_ptr.h"
 #include "base/ref_counted.h"