Keep emtpy List/Dictionary pref value with non-empty default.

chrome/browser/prefs/pref_service_mock_builder.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/prefs/pref_service_mock_builder.h"
 
 #include "base/message_loop_proxy.h"
 #include "chrome/browser/policy/configuration_policy_pref_store.h"
 #include "chrome/browser/prefs/command_line_pref_store.h"
 #include "chrome/browser/prefs/default_pref_store.h"
@@ skipping 59 matching lines @@
 #endif
 
 PrefServiceMockBuilder&
 PrefServiceMockBuilder::WithCommandLine(CommandLine* command_line) {
   command_line_prefs_ = new CommandLinePrefStore(command_line);
   return *this;
 }
 
 PrefServiceMockBuilder&
 PrefServiceMockBuilder::WithUserFilePrefs(const FilePath& prefs_file) {
-  user_prefs_ =
-      new JsonPrefStore(prefs_file,
-                        BrowserThread::GetMessageLoopProxyForThread(
-                            BrowserThread::FILE));
+  return WithUserFilePrefs(prefs_file,
+                           BrowserThread::GetMessageLoopProxyForThread(
+                               BrowserThread::FILE));
+}
+
+PrefServiceMockBuilder&
+PrefServiceMockBuilder::WithUserFilePrefs(
+    const FilePath& prefs_file,
+    base::MessageLoopProxy* message_loop_proxy) {
+  user_prefs_ = new JsonPrefStore(prefs_file, message_loop_proxy);
   return *this;
 }
 
 PrefService* PrefServiceMockBuilder::Create() {
   DefaultPrefStore* default_pref_store = new DefaultPrefStore();
   PrefNotifierImpl* pref_notifier = new PrefNotifierImpl();
   PrefService* pref_service =
       new PrefService(
           pref_notifier,
           new PrefValueStore(
@@ skipping 10 matching lines @@
           NULL,
           false);
   managed_prefs_ = NULL;
   extension_prefs_ = NULL;
   command_line_prefs_ = NULL;
   user_prefs_ = NULL;
   recommended_prefs_ = NULL;
   user_prefs_ = new TestingPrefStore;
   return pref_service;
 }