chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/extension_app_icon_loader.h

 // Copyright 2016 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_EXTENSIONS_EXTENSION_APP_ICON_LOADER_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTENSION_APP_ICON_LOADER_H_
 
 #include <map>
 #include <memory>
 #include <string>
 
 #include "base/macros.h"
 #include "chrome/browser/ui/app_icon_loader.h"
 #include "extensions/browser/extension_icon_image.h"
 
 class Profile;
 
 namespace extensions {
-class Extension;
 
 // Implementation of AppIconLoader that interacts with the ExtensionService and
 // ImageLoader to load images.
 class ExtensionAppIconLoader : public AppIconLoader,
                                public extensions::IconImage::Observer {
  public:
   ExtensionAppIconLoader(Profile* profile, int icon_size,
                          AppIconLoaderDelegate* delegate);
   ~ExtensionAppIconLoader() override;
 
@@ skipping 15 matching lines @@
 
   // Maps from extension id to IconImage pointer.
   ExtensionIDToImageMap map_;
 
   DISALLOW_COPY_AND_ASSIGN(ExtensionAppIconLoader);
 };
 
 }  // namespace extensions
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTENSION_APP_ICON_LOADER_H_