chrome: Cleanup class/struct forward declarations

chrome/browser/ui/webui/signin/signin_error_handler.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_WEBUI_SIGNIN_SIGNIN_ERROR_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SIGNIN_SIGNIN_ERROR_HANDLER_H_
 
 #include <string>
 
 #include "base/files/file_path.h"
 #include "base/macros.h"
 #include "content/public/browser/web_ui_message_handler.h"
 
-class Browser;
-
 namespace base {
 class ListValue;
 }
 
 class SigninErrorHandler : public content::WebUIMessageHandler {
  public:
   explicit SigninErrorHandler(bool is_system_profile);
 
   ~SigninErrorHandler() override {}
 
@@ skipping 34 matching lines @@
 
  private:
   base::FilePath duplicate_profile_path_;
 
   bool is_system_profile_;
 
   DISALLOW_COPY_AND_ASSIGN(SigninErrorHandler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SIGNIN_SIGNIN_ERROR_HANDLER_H_