Cleanup: Fix nits from r156409.

chrome/test/data/extensions/api_test/media_galleries_private/attachdetach/test.js

Index: chrome/test/data/extensions/api_test/media_galleries_private/attachdetach/test.js
===================================================================
--- chrome/test/data/extensions/api_test/media_galleries_private/attachdetach/test.js	(revision 156605)
+++ chrome/test/data/extensions/api_test/media_galleries_private/attachdetach/test.js	(working copy)
@@ -2,18 +2,18 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
-var attached_device_id = '42';
+var attachedDeviceId = '42';
 
 chrome.mediaGalleriesPrivate.onDeviceAttached.addListener(function(details) {
   // Save the device id for the detach test.
-  attached_device_id = details.deviceId;
+  attachedDeviceId = details.deviceId;
   // The C++ test code will check if this is ok.
   chrome.test.sendMessage('attach_test_ok,' + details.deviceName);
 });
 
 chrome.mediaGalleriesPrivate.onDeviceDetached.addListener(function(details) {
   // The C++ test does not know the device id, so check here.
-  if (details.deviceId != attached_device_id) {
+  if (details.deviceId != attachedDeviceId) {
     chrome.test.fail('Bad device id in onDeviceDetached test.');
     return;
   }