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

base/prefs/pref_store_observer_mock.cc

Index: base/prefs/pref_store_observer_mock.cc
diff --git a/base/prefs/pref_store_observer_mock.cc b/base/prefs/pref_store_observer_mock.cc
index 0970e6310d776f29fe40dba381f5c20eb107b54d..4cab6b5047190d676f732b5e4f9e289fc1c64152 100644
--- a/base/prefs/pref_store_observer_mock.cc
+++ b/base/prefs/pref_store_observer_mock.cc
@@ -4,6 +4,16 @@
 
 #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;
+}