Follow up on focus event helper function

[pixelhandler]

@rwjblue there is one other point to chat about at some point too, the focus method in the existing test helpers has an issue with Firefox and focus on window or not. I was able to resolve that in this library as I added test running via Chrome, Firefox on Travis as well.

See…

https://github.com/cibernox/ember-native-dom-helpers/blob/master/addon-test-support/helpers.js#L11-L31

vs.

https://github.com/emberjs/ember.js/blob/7819409b7b6559e9fc0300a29e66a16356fb67a7/packages/ember-testing/lib/events.js#L8-L27

[pixelhandler]

Tests to investigate:

• https://github.com/emberjs/ember.js/blob/7819409b7b6559e9fc0300a29e66a16356fb67a7/packages/ember-testing/tests/helpers_test.js#L696-L728
• https://github.com/emberjs/ember.js/blob/7819409b7b6559e9fc0300a29e66a16356fb67a7/packages/ember-testing/tests/helpers_test.js#L354-L425

These tests failed for us when running on Firefox or phantomjs…

• https://github.com/cibernox/ember-native-dom-helpers/blob/master/tests/integration/fill-in-test.js
• https://github.com/cibernox/ember-native-dom-helpers/blob/master/tests/integration/click-test.js

…the focus part was the issue

Test failure example, focus not firing when window does not have focus:

• https://travis-ci.org/cibernox/ember-native-dom-helpers/jobs/202589665