Add browser tests for USB device add/remove events.

extensions/test/data/api_test/usb/remove_event/background.js

 // 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.
 
 var known_devices = {};
 
-chrome.hid.onDeviceRemoved.addListener(function (deviceId) {
-  if (deviceId in known_devices) {
+chrome.usb.onDeviceRemoved.addListener(function(device) {
+  if (device.device in known_devices) {
     chrome.test.sendMessage("success");
   } else {
-    console.error("Unexpected device removed: " + device.deviceId);
+    console.error("Unexpected device removed: " + device.device);
     chrome.test.sendMessage("failure");
   }
 });
 
-chrome.hid.getDevices({}, function (devices) {
+chrome.usb.getDevices({}, function(devices) {
   for (var device of devices) {
-    known_devices[device.deviceId] = device;
+    known_devices[device.device] = device;
   }
   chrome.test.sendMessage("loaded");
 });