Remove non-MD code from TrayBackgroundView

ash/common/system/web_notification/web_notification_tray.cc

Index: ash/common/system/web_notification/web_notification_tray.cc
diff --git a/ash/common/system/web_notification/web_notification_tray.cc b/ash/common/system/web_notification/web_notification_tray.cc
index 6a2470d36284e35b68d9455f8eff36f17fdb1871..676fcb74dc110ccab4478877946196f4e8ea3e94 100644
--- a/ash/common/system/web_notification/web_notification_tray.cc
+++ b/ash/common/system/web_notification/web_notification_tray.cc
@@ -297,16 +297,15 @@ WebNotificationTray::WebNotificationTray(WmShelf* shelf,
   DCHECK(status_area_window_);
   DCHECK(system_tray_);
 
+  SetContentsBackground();
   if (MaterialDesignController::IsShelfMaterial()) {
     SetInkDropMode(InkDropMode::ON);
-    SetContentsBackground(false);
     gfx::ImageSkia bell_image =
         CreateVectorIcon(kShelfNotificationsIcon, kShelfIconColor);
     const gfx::Size bell_icon_size = kTrayItemInnerIconSize;
     bell_icon_.reset(new WebNotificationImage(
         bell_image, bell_icon_size, animation_container_.get(), this));
   } else {
-    SetContentsBackground(true);
     gfx::ImageSkia bell_image =
         CreateVectorIcon(gfx::VectorIconId::NOTIFICATIONS, kNoUnreadIconSize,
                          kWebNotificationColorNoUnread);