Refactor TestingPrefStore to make it useful to some tests of load errors and asynchrony.

base/prefs/pref_store_observer_mock.cc

 // Copyright (c) 2011 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 "base/prefs/pref_store_observer_mock.h"
 
-PrefStoreObserverMock::PrefStoreObserverMock() {}
+PrefStoreObserverMock::PrefStoreObserverMock()
+    : initialized(false), initialization_success(false) {}
 
 PrefStoreObserverMock::~PrefStoreObserverMock() {}
+
+void PrefStoreObserverMock::OnPrefValueChanged(const std::string& key) {
+  changed_keys.push_back(key);
+}
+
+void PrefStoreObserverMock::OnInitializationCompleted(bool success) {
+  initialized = true;
+  initialization_success = success;
+}