mash: Introduce WmSystemTrayNotifier for //ash/common

ash/common/system/tray/wm_system_tray_notifier.h

Index: ash/common/system/tray/wm_system_tray_notifier.h
diff --git a/ash/common/system/tray/wm_system_tray_notifier.h b/ash/common/system/tray/wm_system_tray_notifier.h
new file mode 100644
index 0000000000000000000000000000000000000000..9931f968f743cc0d56ad776b8a68ce9307a76116
--- /dev/null
+++ b/ash/common/system/tray/wm_system_tray_notifier.h
@@ -0,0 +1,40 @@
+// 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_WM_SYSTEM_TRAY_NOTIFIER_H_
+#define ASH_COMMON_SYSTEM_TRAY_WM_SYSTEM_TRAY_NOTIFIER_H_
+
+#include "ash/ash_export.h"
+#include "base/macros.h"
+#include "base/observer_list.h"
+
+namespace ash {
+
+struct UpdateInfo;
+class UpdateObserver;
+
+// Observer and notification manager for the ash system tray. This version
+// contains the observers that have been ported to //ash/common. See also
+// ash::SystemTrayNotifier.
+// TODO(jamescook): After all the observers have been moved, rename this class
+// to SystemTrayNotifier.
+class ASH_EXPORT WmSystemTrayNotifier {
+ public:
+  WmSystemTrayNotifier();
+  ~WmSystemTrayNotifier();
+
+  void AddUpdateObserver(UpdateObserver* observer);
+  void RemoveUpdateObserver(UpdateObserver* observer);
+
+  void NotifyUpdateRecommended(const UpdateInfo& info);
+
+ private:
+  base::ObserverList<UpdateObserver> update_observers_;
+
+  DISALLOW_COPY_AND_ASSIGN(WmSystemTrayNotifier);
+};
+
+}  // namespace ash
+
+#endif  // ASH_COMMON_SYSTEM_TRAY_WM_SYSTEM_TRAY_NOTIFIER_H_