Notifications: Add cross-platform UMA: ShowMessageCenter, ShowSettings.

ui/message_center/message_center_observer.h

Index: ui/message_center/message_center_observer.h
diff --git a/ui/message_center/message_center_observer.h b/ui/message_center/message_center_observer.h
index da7da21fcb47ccae3974c9811eaefaee464f4c3a..0dcbeee27f6fee2412f86667f18f75e73a730504 100644
--- a/ui/message_center/message_center_observer.h
+++ b/ui/message_center/message_center_observer.h
@@ -7,6 +7,7 @@
 
 #include <string>
 
+#include "ui/message_center/message_center.h"
 #include "ui/message_center/message_center_export.h"
 
 namespace message_center {
@@ -42,9 +43,8 @@ class MESSAGE_CENTER_EXPORT MessageCenterObserver {
   // displayed.
   virtual void OnNotificationDisplayed(const std::string& notification_id) {}
 
-  // Called when the notification list is no longer being displayed as a
-  // notification center.
-  virtual void OnNotificationCenterClosed() {}
+  // Called when the notification center is shown or hidden.
+  virtual void OnCenterVisibilityChanged(Visibility visibility) {}
 
   // Called whenever the quiet mode changes as a result of user action or when
   // quiet mode expires.