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

chrome/browser/prefs/pref_service_mock_builder.h

 // 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.
 
 #ifndef CHROME_BROWSER_PREFS_PREF_SERVICE_MOCK_BUILDER_H_
 #define CHROME_BROWSER_PREFS_PREF_SERVICE_MOCK_BUILDER_H_
 #pragma once
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "chrome/common/persistent_pref_store.h"
 #include "chrome/common/pref_store.h"
 
 class CommandLine;
 class FilePath;
 class PrefService;
 
+namespace base {
+class MessageLoopProxy;
+}
+
 namespace policy {
 class PolicyService;
 }
 
 // A helper that allows convenient building of custom PrefServices in tests.
 class PrefServiceMockBuilder {
  public:
   PrefServiceMockBuilder();
   ~PrefServiceMockBuilder();
 
@@ skipping 11 matching lines @@
       policy::PolicyService* service);
   PrefServiceMockBuilder& WithRecommendedPolicies(
       policy::PolicyService* service);
 #endif
 
   // Specifies to use an actual command-line backed command-line pref store.
   PrefServiceMockBuilder& WithCommandLine(CommandLine* command_line);
 
   // Specifies to use an actual file-backed user pref store.
   PrefServiceMockBuilder& WithUserFilePrefs(const FilePath& prefs_file);
+  PrefServiceMockBuilder& WithUserFilePrefs(
+      const FilePath& prefs_file,
+      base::MessageLoopProxy* message_loop_proxy);
 
   // Creates the PrefService, invalidating the entire builder configuration.
   PrefService* Create();
 
  private:
   scoped_refptr<PrefStore> managed_prefs_;
   scoped_refptr<PrefStore> extension_prefs_;
   scoped_refptr<PrefStore> command_line_prefs_;
   scoped_refptr<PersistentPrefStore> user_prefs_;
   scoped_refptr<PrefStore> recommended_prefs_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefServiceMockBuilder);
 };
 
 #endif  // CHROME_BROWSER_PREFS_PREF_SERVICE_MOCK_BUILDER_H_