chrome: Cleanup class/struct forward declarations

chrome/browser/ui/bookmarks/enhanced_bookmark_key_service_factory.h

 // Copyright 2015 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_BOOKMARKS_ENHANCED_BOOKMARK_KEY_SERVICE_FACTORY_H_
 #define CHROME_BROWSER_UI_BOOKMARKS_ENHANCED_BOOKMARK_KEY_SERVICE_FACTORY_H_
 
 #include "base/macros.h"
 #include "components/keyed_service/content/browser_context_keyed_service_factory.h"
 
 namespace content {
 class BrowserContext;
 }  // namespace content
 
 namespace base {
 template <typename T> struct DefaultSingletonTraits;
 }
 
-class EnhancedBookmarkKeyService;
-
 // Singleton that owns all EnhancedBookmarkKeyServices and associates them with
 // BrowserContexts.
 class EnhancedBookmarkKeyServiceFactory
     : public BrowserContextKeyedServiceFactory {
  public:
   static EnhancedBookmarkKeyServiceFactory* GetInstance();
 
  private:
   friend struct base::DefaultSingletonTraits<EnhancedBookmarkKeyServiceFactory>;
 
   EnhancedBookmarkKeyServiceFactory();
   ~EnhancedBookmarkKeyServiceFactory() override;
 
   // BrowserContextKeyedServiceFactory:
   KeyedService* BuildServiceInstanceFor(
       content::BrowserContext* context) const override;
   content::BrowserContext* GetBrowserContextToUse(
       content::BrowserContext* context) const override;
   bool ServiceIsCreatedWithBrowserContext() const override;
   bool ServiceIsNULLWhileTesting() const override;
 
   DISALLOW_COPY_AND_ASSIGN(EnhancedBookmarkKeyServiceFactory);
 };
 
 #endif  // CHROME_BROWSER_UI_BOOKMARKS_ENHANCED_BOOKMARK_KEY_SERVICE_FACTORY_H_