Fix broken PrefService::preference_set() returning not all registered preferences.

chrome/browser/prefs/value_map_pref_store.cc

Index: chrome/browser/prefs/value_map_pref_store.cc
diff --git a/chrome/browser/prefs/value_map_pref_store.cc b/chrome/browser/prefs/value_map_pref_store.cc
index 705c958b9c0c6ac32695f5c040764cb51bf21dcb..58c401608127e36f1b21142aba5fb5de59084455 100644
--- a/chrome/browser/prefs/value_map_pref_store.cc
+++ b/chrome/browser/prefs/value_map_pref_store.cc
@@ -39,3 +39,19 @@ void ValueMapPrefStore::RemoveValue(const std::string& key) {
 void ValueMapPrefStore::NotifyInitializationCompleted() {
   FOR_EACH_OBSERVER(Observer, observers_, OnInitializationCompleted());
 }
+
+ValueMapPrefStore::iterator ValueMapPrefStore::begin() {
+  return prefs_.begin();
+}
+
+ValueMapPrefStore::iterator ValueMapPrefStore::end() {
+  return prefs_.end();
+}
+
+ValueMapPrefStore::const_iterator ValueMapPrefStore::begin() const {
+  return prefs_.begin();
+}
+
+ValueMapPrefStore::const_iterator ValueMapPrefStore::end() const {
+  return prefs_.end();
+}