Materialized the font/icon color for some default rows in the system menu.

ash/common/system/tray/tray_popup_item_style_observer.h

-// 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.
-
-#ifndef ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_ITEM_STYLE_OBSERVER_H_
-#define ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_ITEM_STYLE_OBSERVER_H_
-
-namespace ash {
-
-class TrayPopupItemStyleObserver {
- public:
-  // Notified by TrayPopupItemStyle instances when the Style is updated (even if
-  // the style values aren't changing).
-  virtual void OnTrayPopupItemStyleUpdated() = 0;
-};
-
-}  // namespace ash
-
-#endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_POPUP_ITEM_STYLE_OBSERVER_H_