Try again to deflake animations/play-state.html

Currently, we use runAnimationTest(), but this can't use the pause API because
it's incompatible with pausing animations through CSS. As a result, it's flaky.

This change re-writes the test to not use runAnimationTest() and to avoid the
need for precise timing,

R=dstockwell

Review URL: https://codereview.chromium.org/38303003

git-svn-id: svn://svn.chromium.org/blink/trunk@160403 bbb929c8-8fbe-4397-9dbb-9b2b20218538