Break two classes defined in json_value_serializer.cc, .h into separate files.

chrome/test/automation/tab_proxy.cc

 // 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.
 
 #include "chrome/test/automation/tab_proxy.h"
 
 #include <algorithm>
 
-#include "base/json/json_value_serializer.h"
+#include "base/json/json_string_value_serializer.h"
 #include "base/logging.h"
 #include "base/string16.h"
 #include "base/threading/platform_thread.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/common/automation_constants.h"
 #include "chrome/common/automation_messages.h"
 #include "chrome/test/automation/automation_json_requests.h"
 #include "chrome/test/automation/automation_proxy.h"
 #include "chrome/test/automation/browser_proxy.h"
 #include "googleurl/src/gurl.h"
@@ skipping 818 matching lines @@
                                                       json));
 }
 
 void TabProxy::FirstObjectAdded() {
   AddRef();
 }
 
 void TabProxy::LastObjectRemoved() {
   Release();
 }