Remove usage of FOR_EACH_OBSERVER macro in ash/common

ash/common/wallpaper/wallpaper_controller.cc

Index: ash/common/wallpaper/wallpaper_controller.cc
diff --git a/ash/common/wallpaper/wallpaper_controller.cc b/ash/common/wallpaper/wallpaper_controller.cc
index 76864c6e04b3de1c6a3b1327fbf7f783a713ca59..895f47101c0922705a1568e0c2b2ef7b211d06c9 100644
--- a/ash/common/wallpaper/wallpaper_controller.cc
+++ b/ash/common/wallpaper/wallpaper_controller.cc
@@ -79,8 +79,8 @@ bool WallpaperController::SetWallpaperImage(const gfx::ImageSkia& image,
       image, GetMaxDisplaySizeInNative(), layout, task_runner_));
   current_wallpaper_->StartResize();
 
-  FOR_EACH_OBSERVER(WallpaperControllerObserver, observers_,
-                    OnWallpaperDataChanged());
+  for (auto& observer : observers_)
+    observer.OnWallpaperDataChanged();
   wallpaper_mode_ = WALLPAPER_IMAGE;
   InstallDesktopControllerForAllWindows();
   return true;