Cleanup: Remove unneeded forward declarations from chrome/browser/extensions.

chrome/browser/extensions/external_extension_provider_impl.h

 // Copyright (c) 2011 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_EXTERNAL_EXTENSION_PROVIDER_IMPL_H_
 #define CHROME_BROWSER_EXTENSIONS_EXTERNAL_EXTENSION_PROVIDER_IMPL_H_
 #pragma once
 
+#include <string>
+
 #include "chrome/browser/extensions/external_extension_provider_interface.h"
 
 #include "base/memory/ref_counted.h"
 #include "chrome/browser/extensions/external_extension_loader.h"
 
 class ExternalExtensionLoader;
 class Profile;
 class Version;
 
 namespace base {
 class DictionaryValue;
-class ValueSerializer;
 }
 
 // A specialization of the ExternalExtensionProvider that uses an instance
 // of ExternalExtensionLoader to provide external extensions. This class
 // can be seen as a bridge between the extension system and an
 // ExternalExtensionLoader. Instances live their entire life on the UI thread.
 class ExternalExtensionProviderImpl
     : public ExternalExtensionProviderInterface {
  public:
   // The constructed provider will provide the extensions loaded from |loader|
@@ skipping 64 matching lines @@
   scoped_refptr<ExternalExtensionLoader> loader_;
 
   // Creation flags to use for the extension.  These flags will be used
   // when calling Extenion::Create() by the crx installer.
   int creation_flags_;
 
   DISALLOW_COPY_AND_ASSIGN(ExternalExtensionProviderImpl);
 };
 
 #endif  // CHROME_BROWSER_EXTENSIONS_EXTERNAL_EXTENSION_PROVIDER_IMPL_H_