Implement message center on Windows

ui/message_center/message_center.cc

Index: ui/message_center/message_center.cc
diff --git a/ui/message_center/message_center.cc b/ui/message_center/message_center.cc
index 394dab9ff3739015b88a7b4474d22aa86a41342a..76344ef013992ebf68ccd9e6444c06132142b25b 100644
--- a/ui/message_center/message_center.cc
+++ b/ui/message_center/message_center.cc
@@ -12,9 +12,9 @@ namespace message_center {
 
 //------------------------------------------------------------------------------
 
-// static
-MessageCenter* MessageCenter::GetInstance() {
-  return Singleton<MessageCenter>::get();
+MessageCenter::MessageCenter()
+    : delegate_(NULL) {
+  notification_list_.reset(new NotificationList(this));
 }
 
 MessageCenter::~MessageCenter() {
@@ -172,11 +172,6 @@ void MessageCenter::Delegate::OnButtonClicked(const std::string& id,
 //------------------------------------------------------------------------------
 // Private.
 
-MessageCenter::MessageCenter()
-    : delegate_(NULL) {
-  notification_list_.reset(new NotificationList(this));
-}
-
 void MessageCenter::NotifyMessageCenterChanged(bool new_notification) {
   FOR_EACH_OBSERVER(Observer,
                     observer_list_,