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

chrome/browser/extensions/api/webrequest/webrequest_api_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 <queue>
 #include <map>
 
 #include "base/bind.h"
 #include "base/callback.h"
 #include "base/file_util.h"
-#include "base/json/json_value_serializer.h"
+#include "base/json/json_string_value_serializer.h"
 #include "base/memory/weak_ptr.h"
 #include "base/path_service.h"
 #include "base/stl_util.h"
 #include "base/utf_string_conversions.h"
 #include "chrome/browser/extensions/api/webrequest/webrequest_api.h"
 #include "chrome/browser/extensions/api/webrequest/webrequest_api_constants.h"
 #include "chrome/browser/extensions/api/webrequest/webrequest_api_helpers.h"
 #include "chrome/browser/extensions/extension_event_router_forwarder.h"
 #include "chrome/browser/net/chrome_network_delegate.h"
 #include "chrome/browser/prefs/pref_member.h"
@@ skipping 1391 matching lines @@
   credentials_set = MergeOnAuthRequiredResponses(
         deltas, &auth3, &conflicting_extensions, &event_log);
   EXPECT_TRUE(credentials_set);
   EXPECT_FALSE(auth3.Empty());
   EXPECT_EQ(username, auth1.username());
   EXPECT_EQ(password, auth1.password());
   EXPECT_EQ(1u, conflicting_extensions.size());
   EXPECT_TRUE(ContainsKey(conflicting_extensions, "extid2"));
   EXPECT_EQ(3u, event_log.size());
 }