Remove FOR_EACH_OBSERVER from arc/ since it's being deprecated

ui/arc/notification/arc_notification_surface_manager.cc

Index: ui/arc/notification/arc_notification_surface_manager.cc
diff --git a/ui/arc/notification/arc_notification_surface_manager.cc b/ui/arc/notification/arc_notification_surface_manager.cc
index d816da8a234891c50acc7f88446cccabfb03685f..dbc03b45a3a8a6504731b674c2133e8fd2a7fb8f 100644
--- a/ui/arc/notification/arc_notification_surface_manager.cc
+++ b/ui/arc/notification/arc_notification_surface_manager.cc
@@ -47,7 +47,8 @@ void ArcNotificationSurfaceManager::AddSurface(
 
   notification_surface_map_[surface->notification_id()] = surface;
 
-  FOR_EACH_OBSERVER(Observer, observers_, OnNotificationSurfaceAdded(surface));
+  for (auto& observer : observers_)
+    observer.OnNotificationSurfaceAdded(surface);
 }
 
 void ArcNotificationSurfaceManager::RemoveSurface(
@@ -57,8 +58,8 @@ void ArcNotificationSurfaceManager::RemoveSurface(
     return;
 
   notification_surface_map_.erase(it);
-  FOR_EACH_OBSERVER(Observer, observers_,
-                    OnNotificationSurfaceRemoved(surface));
+  for (auto& observer : observers_)
+    observer.OnNotificationSurfaceRemoved(surface);
 }
 
 void ArcNotificationSurfaceManager::AddObserver(Observer* observer) {