fast/images/animated-gif-body-outside-viewport.html is flaky
https://bugs.webkit.org/show_bug.cgi?id=139599

Reviewed by Alexey Proskuryakov.

Update fast/images/animated-gif-body-outside-viewport.html to use
shouldBecomeEqual() instead of a setTimeout() + shouldBe() to fix
the flakiness.

* fast/images/animated-gif-body-outside-viewport-expected.txt:
* fast/images/animated-gif-body-outside-viewport.html:
* platform/mac-wk1/TestExpectations:


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@177265 268f45cc-cd09-0410-ab3c-d52691b4dbfc