ash: Cleanup class/struct forward declarations

ash/common/system/web_notification/web_notification_tray.h

Index: ash/common/system/web_notification/web_notification_tray.h
diff --git a/ash/common/system/web_notification/web_notification_tray.h b/ash/common/system/web_notification/web_notification_tray.h
index a22a4bcfa9e2c8936eab91fa87940e5b28f1c41a..fb2a72d342986a34fa3a8f481b0d7cb871be8ef3 100644
--- a/ash/common/system/web_notification/web_notification_tray.h
+++ b/ash/common/system/web_notification/web_notification_tray.h
@@ -27,12 +27,7 @@
 // generated by SystemTrayItem). Visibility of one notification type or other
 // is controlled by StatusAreaWidget.
 
-namespace views {
-class MenuRunner;
-}
-
 namespace message_center {
-class MessageBubbleBase;
 class MessageCenter;
 class MessageCenterBubble;
 class MessagePopupCollection;
@@ -42,7 +37,6 @@ namespace ash {
 class AshPopupAlignmentDelegate;
 class SystemTray;
 class WebNotificationBubbleWrapper;
-class WebNotificationButton;
 class WebNotificationImage;
 class WebNotificationLabel;
 class WmWindow;