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

chrome/browser/sync/profile_sync_service_preference_unittest.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 <map>
 #include <string>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/callback.h"
 #include "base/json/json_reader.h"
-#include "base/json/json_value_serializer.h"
+#include "base/json/json_string_value_serializer.h"
 #include "base/location.h"
 #include "base/stl_util.h"
 #include "base/string_piece.h"
 #include "chrome/browser/prefs/pref_model_associator.h"
 #include "chrome/browser/prefs/scoped_user_pref_update.h"
 #include "chrome/browser/signin/signin_manager.h"
 #include "chrome/browser/signin/signin_manager_factory.h"
 #include "chrome/browser/signin/token_service.h"
 #include "chrome/browser/sync/abstract_profile_sync_service_test.h"
 #include "chrome/browser/sync/api/sync_data.h"
@@ skipping 562 matching lines @@
   EXPECT_FALSE(pref->IsDefaultValue());
   // There should be no synced value.
   EXPECT_TRUE(GetSyncedValue(prefs::kHomePage) == NULL);
   // Switch kHomePage back to unmanaged.
   profile_->GetTestingPrefService()->RemoveManagedPref(prefs::kHomePage);
   // The original value should be picked up.
   EXPECT_TRUE(pref->IsDefaultValue());
   // There should still be no synced value.
   EXPECT_TRUE(GetSyncedValue(prefs::kHomePage) == NULL);
 }