Fix Layout Test pointer-lock/locked-element-removed-from-dom.html flakiness.

https://bugs.webkit.org/show_bug.cgi?id=91373

Reviewed by Adrienne Walker.

pointer-lock-test-harness corrected to no longer silently allow too many
asynchronous doNextStep calls in a test. The locked-element-removed-from-dom test
generated too many events and incorrectly exited the test early.

* platform/chromium/TestExpectations:
    Re-enabled locked-element-removed-from-dom test.html
* pointer-lock/locked-element-removed-from-dom.html:
    Absorb extra doNextStep.
* pointer-lock/resources/pointer-lock-test-harness.js:
(doNextStep.setTimeout):
    Fail tests that call doNextStep too many times.


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@122758 268f45cc-cd09-0410-ab3c-d52691b4dbfc