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

chrome/browser/extensions/sandboxed_extension_unpacker.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/browser/extensions/sandboxed_extension_unpacker.h"
 
 #include <set>
 
 #include "base/base64.h"
 #include "base/bind.h"
 #include "base/file_util.h"
 #include "base/file_util_proxy.h"
-#include "base/json/json_value_serializer.h"
+#include "base/json/json_string_value_serializer.h"
 #include "base/memory/scoped_handle.h"
 #include "base/message_loop.h"
 #include "base/metrics/histogram.h"
 #include "base/path_service.h"
 #include "base/utf_string_conversions.h"  // TODO(viettrungluu): delete me.
 #include "chrome/browser/extensions/extension_service.h"
 #include "chrome/common/chrome_paths.h"
 #include "chrome/common/chrome_switches.h"
 #include "chrome/common/chrome_utility_messages.h"
 #include "chrome/common/extensions/extension_constants.h"
@@ skipping 753 matching lines @@
           ERROR_SAVING_CATALOG,
           l10n_util::GetStringFUTF16(
               IDS_EXTENSION_PACKAGE_INSTALL_ERROR,
               ASCIIToUTF16("ERROR_SAVING_CATALOG")));
       return false;
     }
   }
 
   return true;
 }