Remove FOR_EACH_OBSERVER from arc/ since it's being deprecated

ui/arc/notification/arc_notification_surface_manager.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/arc/notification/arc_notification_surface_manager.h"
 
 #include <algorithm>
 
 #include "components/exo/notification_surface.h"
 
@@ skipping 29 matching lines @@
 void ArcNotificationSurfaceManager::AddSurface(
     exo::NotificationSurface* surface) {
   if (notification_surface_map_.find(surface->notification_id()) !=
       notification_surface_map_.end()) {
     NOTREACHED();
     return;
   }
 
   notification_surface_map_[surface->notification_id()] = surface;
 
-  FOR_EACH_OBSERVER(Observer, observers_, OnNotificationSurfaceAdded(surface));
+  for (auto& observer : observers_)
+    observer.OnNotificationSurfaceAdded(surface);
 }
 
 void ArcNotificationSurfaceManager::RemoveSurface(
     exo::NotificationSurface* surface) {
   auto it = notification_surface_map_.find(surface->notification_id());
   if (it == notification_surface_map_.end())
     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) {
   observers_.AddObserver(observer);
 }
 
 void ArcNotificationSurfaceManager::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
 }  // namespace arc