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

chrome/browser/prefs/testing_pref_store.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/testing_pref_store.h"
 
 #include "base/values.h"
 
 TestingPrefStore::TestingPrefStore()
     : read_only_(true),
@@ skipping 35 matching lines @@
 
 void TestingPrefStore::SetValueSilently(const std::string& key, Value* value) {
   prefs_.SetValue(key, value);
 }
 
 void TestingPrefStore::RemoveValue(const std::string& key) {
   if (prefs_.RemoveValue(key))
     NotifyPrefValueChanged(key);
 }
 
+void TestingPrefStore::MarkNeedsEmptyValue(const std::string& key) {
+}
+
 bool TestingPrefStore::ReadOnly() const {
   return read_only_;
 }
 
 PersistentPrefStore::PrefReadError TestingPrefStore::GetReadError() const {
   return PersistentPrefStore::PREF_READ_ERROR_NONE;
 }
 
 PersistentPrefStore::PrefReadError TestingPrefStore::ReadPrefs() {
   prefs_.Clear();
@@ skipping 58 matching lines @@
   const Value* stored_value;
   if (!prefs_.GetValue(key, &stored_value) || !stored_value)
     return false;
 
   return stored_value->GetAsBoolean(value);
 }
 
 void TestingPrefStore::set_read_only(bool read_only) {
   read_only_ = read_only;
 }