bluetooth: Add DeviceChanged logging in Device service.

device/bluetooth/public/interfaces/adapter.mojom

 // 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.
 
 module bluetooth.mojom;
 
 import "device/bluetooth/public/interfaces/device.mojom";
 
 struct AdapterInfo {
   string address;
@@ skipping 20 matching lines @@
   // Sets the client that listens for the adapter's events.
   SetClient(AdapterClient client);
 };
 
 interface AdapterClient {
   // Called the first time a device is discovered.
   DeviceAdded(DeviceInfo device);
 
   // Called after the device hasn't been seen for 3 minutes.
   DeviceRemoved(DeviceInfo device);
+
+  // Called when one of the following properties of a device changes:
+  //   Address, appearance, Bluetooth class, Inquiry RSSI, Inquiry TX Power,
+  //   Service UUIDs, Connectionable state, Connection state, Pairing state,
+  //   Trustable state.
+  // Generally called for each advertisement packet recevied, but this is not
+  // guaranteed on ChromeOS or Linux. Because the RSSI is always changing,
+  // it's very likely this will be called for each advertising packet.
+  DeviceChanged(DeviceInfo device);
 };
 
 interface AdapterFactory {
   // Gets an Adapter interface. Returns null if Bluetooth is not supported.
   GetAdapter() => (Adapter? adapter);
 };