Adds a first-run balloon to the Windows notification center.

ui/message_center/message_center_tray_delegate.h

Index: ui/message_center/message_center_tray_delegate.h
diff --git a/ui/message_center/message_center_tray_delegate.h b/ui/message_center/message_center_tray_delegate.h
index f95fb0a0667fb8b20f15f11ad4b99ac690d93777..41d913258b2e5170b9e59e5c6c7dd74a8d1a8e42 100644
--- a/ui/message_center/message_center_tray_delegate.h
+++ b/ui/message_center/message_center_tray_delegate.h
@@ -35,6 +35,10 @@ class MESSAGE_CENTER_EXPORT MessageCenterTrayDelegate {
 
   // Remove the message center from the UI.
   virtual void HideMessageCenter() = 0;
+
+  // Show a platform-specific UI that informs the user how to open the message
+  // center.
+  virtual void DisplayFirstRunBalloon() {};
 };
 
 }  // namespace message_center