chrome: Cleanup class/struct forward declarations

chrome/browser/ui/views/new_back_shortcut_bubble.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_UI_VIEWS_NEW_BACK_SHORTCUT_BUBBLE_H_
 #define CHROME_BROWSER_UI_VIEWS_NEW_BACK_SHORTCUT_BUBBLE_H_
 
 #include <memory>
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "base/timer/timer.h"
 #include "ui/gfx/animation/animation_delegate.h"
 
 class ExclusiveAccessBubbleViewsContext;
 class SubtleNotificationView;
 
 namespace gfx {
 class Animation;
 class Rect;
 class SlideAnimation;
 }
 
 namespace views {
-class View;
 class Widget;
 }
 
 // NewBackShortcutBubble shows a short-lived notification along the top of the
 // screen when the user presses the old Back/Forward shortcut, telling them how
 // to use the new shortcut. This will only be available for a few milestones to
 // let users adapt.
 // TODO(mgiuca): Remove this in M54 (https://crbug.com/610039).
 class NewBackShortcutBubble : public gfx::AnimationDelegate {
  public:
@@ skipping 28 matching lines @@
 
   // The contents of the popup.
   SubtleNotificationView* const view_;
 
   views::Widget* const popup_;
 
   DISALLOW_COPY_AND_ASSIGN(NewBackShortcutBubble);
 };
 
 #endif  // CHROME_BROWSER_UI_VIEWS_NEW_BACK_SHORTCUT_BUBBLE_H_