chrome: Cleanup class/struct forward declarations

chrome/browser/banners/app_banner_infobar_delegate_desktop.h

 // Copyright 2015 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_BANNERS_APP_BANNER_INFOBAR_DELEGATE_DESKTOP_H_
 #define CHROME_BROWSER_BANNERS_APP_BANNER_INFOBAR_DELEGATE_DESKTOP_H_
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "base/strings/string16.h"
 #include "components/infobars/core/confirm_infobar_delegate.h"
 #include "content/public/common/manifest.h"
 
 namespace content {
 class WebContents;
 }
 
 namespace extensions {
 class BookmarkAppHelper;
-class Extension;
 }
 
 namespace infobars {
 class InfoBar;
 }
 
 namespace banners {
 
 class AppBannerManager;
 
@@ skipping 30 matching lines @@
   content::Manifest manifest_;
   int event_request_id_;
   bool has_user_interaction_;
 
   DISALLOW_COPY_AND_ASSIGN(AppBannerInfoBarDelegateDesktop);
 };
 
 }  // namespace banners
 
 #endif  // CHROME_BROWSER_BANNERS_APP_BANNER_INFOBAR_DELEGATE_DESKTOP_H_