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 02c0ddf74652ac8c6503a3e2a125f53d252a1a2b..3ef35abfa592986ede670859f7546d498a249be2 100644
--- a/ui/message_center/message_center_tray_delegate.h
+++ b/ui/message_center/message_center_tray_delegate.h
@@ -38,6 +38,10 @@ class MESSAGE_CENTER_EXPORT MessageCenterTrayDelegate {
 
   // Display the notifier settings as a bubble.
   virtual bool ShowNotifierSettings() = 0;
+
+  // Show a platform-specific UI that informs the user how to open the message
+  // center.
+  virtual void DisplayFirstRunBalloon() {};
 };
 
 }  // namespace message_center