Port BatteryMonitor into Device Service

device/battery/battery_monitor.mojom

 // Copyright 2014 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.
 
+// TODO(blundell): Move module to device.mojom, and move the mojom files to
+// //device/battery/public/interfaces.
 module device;
 
 import "device/battery/battery_status.mojom";
 
 interface BatteryMonitor {
   // Battery status is reported once it changes or immediately if this is the
   // first call to QueryNextStatus on this instance. QueryNextStatus calls may
   // be throttled by the service. Overlapping calls to QueryNextStatus are
   // prohibited and will be treated as a connection error.
   QueryNextStatus() => (BatteryStatus status);
 };