chrome: Cleanup class/struct forward declarations

chrome/browser/ui/webui/bidi_checker_web_ui_test.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_WEBUI_BIDI_CHECKER_WEB_UI_TEST_H_
 #define CHROME_BROWSER_UI_WEBUI_BIDI_CHECKER_WEB_UI_TEST_H_
 
 #include "base/command_line.h"
 #include "chrome/test/base/web_ui_browser_test.h"
 
-namespace base {
-class WaitableEvent;
-}
-
 // Base class for BidiChecker-based tests. Preloads the BidiChecker JS library
 // for each test.
 class WebUIBidiCheckerBrowserTest : public WebUIBrowserTest {
  public:
   ~WebUIBidiCheckerBrowserTest() override;
 
   // testing::Test implementation.
   void SetUp() override;
   void TearDown() override;
 
@@ skipping 29 matching lines @@
 
  protected:
   void SetUpOnMainThread() override;
   void TearDownOnMainThread() override;
 
   // The app locale before we change it
   std::string app_locale_;
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_BIDI_CHECKER_WEB_UI_TEST_H_