Add browser tests for USB device add/remove events.

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

Index: extensions/test/data/api_test/usb/remove_event/background.js
diff --git a/extensions/test/data/api_test/hid/remove_event/background.js b/extensions/test/data/api_test/usb/remove_event/background.js
similarity index 58%
copy from extensions/test/data/api_test/hid/remove_event/background.js
copy to extensions/test/data/api_test/usb/remove_event/background.js
index ea71668471e665c52e1350c51d52ac45ee69ad1a..22021ed4ec16e5d2b7be42beaac44629c183e983 100644
--- a/extensions/test/data/api_test/hid/remove_event/background.js
+++ b/extensions/test/data/api_test/usb/remove_event/background.js
@@ -4,18 +4,18 @@
 
 var known_devices = {};
 
-chrome.hid.onDeviceRemoved.addListener(function (deviceId) {
-  if (deviceId in known_devices) {
+chrome.usb.onDeviceRemoved.addListener(function (device) {

[Yoyo Zhou, 2015/01/21 06:57:43]

ditto in this file

[Reilly Grant (use Gerrit), 2015/01/22 00:45:01]

Done.

+  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");
 });