Observes work area change and auto-hide for notifications.

ash/system/web_notification/web_notification_tray.h

Index: ash/system/web_notification/web_notification_tray.h
diff --git a/ash/system/web_notification/web_notification_tray.h b/ash/system/web_notification/web_notification_tray.h
index 15c064225fa1b49db97f011c99ddd5fb9a3d4f35..7ebdd5803e9969ffad941065f73e771f359af8b6 100644
--- a/ash/system/web_notification/web_notification_tray.h
+++ b/ash/system/web_notification/web_notification_tray.h
@@ -37,11 +37,11 @@ class MessagePopupCollection;
 }
 
 namespace ash {
-
 namespace internal {
 class StatusAreaWidget;
 class WebNotificationBubbleWrapper;
 class WebNotificationButton;
+class WorkAreaObserver;
 }
 
 class ASH_EXPORT WebNotificationTray
@@ -159,6 +159,9 @@ class ASH_EXPORT WebNotificationTray
   // flickers of the shelf from hidden to shown. See: crbug.com/181213
   bool should_block_shelf_auto_hide_;
 
+  // Observes the work area for |popup_collection_| and notifies to it.
+  scoped_ptr<internal::WorkAreaObserver> work_area_observer_;
+
   DISALLOW_COPY_AND_ASSIGN(WebNotificationTray);
 };