chrome: Cleanup class/struct forward declarations

chrome/browser/ui/javascript_dialogs/javascript_dialog_tab_helper.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_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_
 #define CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_
 
 #include <memory>
 
 #include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
 #include "chrome/browser/ui/browser_list_observer.h"
 #include "chrome/browser/ui/javascript_dialogs/javascript_dialog.h"
 #include "content/public/browser/javascript_dialog_manager.h"
 #include "content/public/browser/web_contents_observer.h"
 #include "content/public/browser/web_contents_user_data.h"
 
-class JavaScriptDialogViews;
-
 // A class, attached to WebContentses in browser windows, that is the
 // JavaScriptDialogManager for them and handles displaying their dialogs.
 //
 // This is the primary mechanism for implementing auto-dismissing dialogs,
 // dialogs that close when the user switches away to a different tab. Because
 // JavaScript dialogs are synchronous and block arbitrary sets of renderers,
 // they cannot be made tab-modal. Therefore the next best option is to make them
 // auto-closing, so that they never block the user's access to other renderers.
 //
 // See http://bit.ly/project-oldspice for more details. Note that only part
@@ skipping 55 matching lines @@
   // itself calls it, but in the cases where the dialog is closed not by the
   // user's input but by a call to |CloseDialog|, this class will call it.
   content::JavaScriptDialogManager::DialogClosedCallback dialog_callback_;
 
   base::Closure dialog_shown_;
 
   DISALLOW_COPY_AND_ASSIGN(JavaScriptDialogTabHelper);
 };
 
 #endif  // CHROME_BROWSER_UI_JAVASCRIPT_DIALOGS_JAVASCRIPT_DIALOG_TAB_HELPER_H_