chrome: Cleanup class/struct forward declarations

chrome/browser/ui/android/view_android_helper.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_UI_ANDROID_VIEW_ANDROID_HELPER_H_
 #define CHROME_BROWSER_UI_ANDROID_VIEW_ANDROID_HELPER_H_
 
 #include "base/macros.h"
 #include "content/public/browser/web_contents_user_data.h"
 
-namespace ui {
-class WindowAndroid;
-}
-
 // Per-tab class to provide access to ViewAndroid object.
 class ViewAndroidHelper
     : public content::WebContentsUserData<ViewAndroidHelper> {
  public:
   ~ViewAndroidHelper() override;
 
   void SetViewAndroid(ui::ViewAndroid* view_android);
   ui::ViewAndroid* GetViewAndroid();
 
  private:
   explicit ViewAndroidHelper(content::WebContents* web_contents);
   friend class content::WebContentsUserData<ViewAndroidHelper>;
 
   // The owning view that has a hold of the current window.
   ui::ViewAndroid* view_android_;
 
   DISALLOW_COPY_AND_ASSIGN(ViewAndroidHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_ANDROID_VIEW_ANDROID_HELPER_H_