chrome: Cleanup class/struct forward declarations

chrome/browser/extensions/chrome_extension_test_notification_observer.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_EXTENSIONS_CHROME_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_
 #define CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_
 
 #include <string>
 
 #include "base/macros.h"
 #include "chrome/browser/extensions/api/extension_action/extension_action_api.h"
 #include "extensions/test/extension_test_notification_observer.h"
 
 class Browser;
 
 namespace content {
 class BrowserContext;
-class WindowedNotificationObserver;
 }
 
 // Test helper class for observing extension-related events.
 // TODO(devlin): This should be in the extensions namespace.
 class ChromeExtensionTestNotificationObserver
     : public ExtensionTestNotificationObserver,
       public extensions::ExtensionActionAPI::Observer {
  public:
   explicit ChromeExtensionTestNotificationObserver(Browser* browser);
   ~ChromeExtensionTestNotificationObserver() override;
@@ skipping 18 matching lines @@
 
   // extensions::ExtensionActionAPI::Observer:
   void OnPageActionsUpdated(content::WebContents* contents) override;
 
   Browser* browser_;
 
   DISALLOW_COPY_AND_ASSIGN(ChromeExtensionTestNotificationObserver);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_CHROME_EXTENSION_TEST_NOTIFICATION_OBSERVER_H_