ui: Cleanup class/struct forward declarations

ui/app_list/views/app_list_main_view.h

 // Copyright 2013 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 UI_APP_LIST_VIEWS_APP_LIST_MAIN_VIEW_H_
 #define UI_APP_LIST_VIEWS_APP_LIST_MAIN_VIEW_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "base/memory/scoped_vector.h"
 #include "base/memory/weak_ptr.h"
 #include "base/timer/timer.h"
 #include "ui/app_list/app_list_export.h"
 #include "ui/app_list/app_list_model_observer.h"
 #include "ui/app_list/views/apps_grid_view_delegate.h"
 #include "ui/app_list/views/search_box_view_delegate.h"
 #include "ui/app_list/views/search_result_list_view_delegate.h"
 #include "ui/views/view.h"
 
-namespace views {
-class Widget;
-}
-
 namespace app_list {
 
 class AppListItem;
 class AppListModel;
 class AppListViewDelegate;
 class ApplicationDragAndDropHost;
 class ContentsView;
 class PaginationModel;
 class SearchBoxView;
 
@@ skipping 86 matching lines @@
   ScopedVector<IconLoader> pending_icon_loaders_;
 
   base::WeakPtrFactory<AppListMainView> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(AppListMainView);
 };
 
 }  // namespace app_list
 
 #endif  // UI_APP_LIST_VIEWS_APP_LIST_MAIN_VIEW_H_