chrome: Cleanup class/struct forward declarations

chrome/browser/themes/browser_theme_pack.h

 // Copyright (c) 2012 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_THEMES_BROWSER_THEME_PACK_H_
 #define CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_
 
 #include <stdint.h>
 
 #include <map>
 #include <memory>
 #include <string>
 #include <vector>
 
 #include "base/macros.h"
 #include "base/sequenced_task_runner_helpers.h"
 #include "chrome/browser/themes/custom_theme_supplier.h"
 #include "extensions/common/extension.h"
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/layout.h"
 #include "ui/gfx/color_utils.h"
 
 namespace base {
 class DictionaryValue;
 class FilePath;
 class RefCountedMemory;
 }
 
-namespace extensions {
-class Extensions;
-}
-
 namespace gfx {
 class Image;
 }
 
 namespace ui {
 class DataPack;
 }
 
 // An optimized representation of a theme, backed by a mmapped DataPack.
 //
@@ skipping 222 matching lines @@
   // Cache of images created in BuildFromExtension(). Once the theme pack is
   // created, this cache should only be accessed on the file thread. There
   // should be no IDs in |image_memory_| that are in |images_on_file_thread_|
   // or vice versa.
   ImageCache images_on_file_thread_;
 
   DISALLOW_COPY_AND_ASSIGN(BrowserThemePack);
 };
 
 #endif  // CHROME_BROWSER_THEMES_BROWSER_THEME_PACK_H_