chrome: Cleanup class/struct forward declarations

chrome/browser/ui/signin_view_controller_delegate.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_SIGNIN_VIEW_CONTROLLER_DELEGATE_H_
 #define CHROME_BROWSER_UI_SIGNIN_VIEW_CONTROLLER_DELEGATE_H_
 
 #include "chrome/browser/ui/profile_chooser_constants.h"
 #include "content/public/browser/web_contents_delegate.h"
 
 class Browser;
-class ModalSigninDelegate;
 class SigninViewController;
 
 namespace signin_metrics {
 enum class AccessPoint;
 }
 
 // Abstract base class to the platform-specific managers of the Signin and Sync
 // confirmation tab-modal dialogs. This and its platform-specific
 // implementations are responsible for actually creating and owning the dialogs,
 // as well as managing the navigation inside them.
@@ skipping 61 matching lines @@
 
  private:
   bool CanGoBack(content::WebContents* web_ui_web_contents) const;
 
   SigninViewController* signin_view_controller_;  // Not owned.
   content::WebContents* web_contents_;  // Not owned.
   DISALLOW_COPY_AND_ASSIGN(SigninViewControllerDelegate);
 };
 
 #endif  // CHROME_BROWSER_UI_SIGNIN_VIEW_CONTROLLER_DELEGATE_H_