chrome: Cleanup class/struct forward declarations

chrome/browser/ui/webui/settings/browser_lifetime_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_SETTINGS_BROWSER_LIFETIME_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_SETTINGS_BROWSER_LIFETIME_HANDLER_H_
 
 #include "base/macros.h"
 #include "chrome/browser/ui/webui/settings/settings_page_ui_handler.h"
 
 namespace base {
 class ListValue;
 }
 
-namespace content {
-class WebUIDataSource;
-}
-
 namespace settings {
 
 class BrowserLifetimeHandler : public SettingsPageUIHandler {
  public:
   BrowserLifetimeHandler();
   ~BrowserLifetimeHandler() override;
 
   // SettingsPageUIHandler:
   void RegisterMessages() override;
   void OnJavascriptAllowed() override {}
   void OnJavascriptDisallowed() override {}
 
  private:
   void HandleRestart(const base::ListValue* /*args*/);
   void HandleRelaunch(const base::ListValue* /*args*/);
 #if defined(OS_CHROMEOS)
   void HandleSignOutAndRestart(const base::ListValue* /*args*/);
   void HandleFactoryReset(const base::ListValue* /*args*/);
 #endif  // defined(OS_CHROMEOS)
 
   DISALLOW_COPY_AND_ASSIGN(BrowserLifetimeHandler);
 };
 
 }  // namespace settings
 
 #endif  // CHROME_BROWSER_UI_WEBUI_SETTINGS_BROWSER_LIFETIME_HANDLER_H_