Cleanup: Remove unneeded forward declarations in chrome/browser/sync.

chrome/browser/sync/internal_api/write_node.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_SYNC_INTERNAL_API_WRITE_NODE_H_
 #define CHROME_BROWSER_SYNC_INTERNAL_API_WRITE_NODE_H_
 #pragma once
 
 #include <string>
 #include <vector>
@@ skipping 14 matching lines @@
 
 namespace sync_pb {
 class AppSpecifics;
 class AutofillSpecifics;
 class AutofillProfileSpecifics;
 class BookmarkSpecifics;
 class EntitySpecifics;
 class ExtensionSpecifics;
 class SessionSpecifics;
 class NigoriSpecifics;
-class PreferenceSpecifics;
 class PasswordSpecificsData;
 class ThemeSpecifics;
 class TypedUrlSpecifics;
 }
 
 namespace sync_api {
 
 class WriteTransaction;
 
 // WriteNode extends BaseNode to add mutation, and wraps
@@ skipping 142 matching lines @@
 
   // The sync API transaction that is the parent of this node.
   WriteTransaction* transaction_;
 
   DISALLOW_COPY_AND_ASSIGN(WriteNode);
 };
 
 }  // namespace sync_api
 
 #endif  // CHROME_BROWSER_SYNC_INTERNAL_API_WRITE_NODE_H_