ash: Add a bluetooth entry in the uber tray.

ash/system/bluetooth/bluetooth_observer.h

+// Copyright (c) 2012 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_SYSTEM_BLUETOOTH_BLUETOOTH_OBSERVER_H_
+#define ASH_SYSTEM_BLUETOOTH_BLUETOOTH_OBSERVER_H_
+#pragma once
+
+namespace ash {
+
+class BluetoothObserver {
+ public:
+  virtual ~BluetoothObserver() {}
+
+  virtual void OnBluetoothRefresh() = 0;
+};
+
+}  // namespace ash
+
+#endif  // ASH_SYSTEM_BLUETOOTH_BLUETOOTH_OBSERVER_H_