Rewrite change-values-during-transition.html to be not flaky

The test change-values-during-transition.html is current marked as
WontFix, and flaky in the Web Animations CSS virtual test suite.
The flakiness seems to have been from spinning up the gpu process
which takes ~300ms in the middle of the javascript execution (i.e.
when the transition is started).
I've rewritten the test to use the animation/transition test
framework, using RAF since we start transitions sequentially, and
renamed it to better describe what it's doing. The rewritten version
shouldn't be flaky since the times picks are sufficient to allow the
gpu process to spin up, and we transition left so we probably won't
spin it up in the first place.

BUG=

Review URL: https://codereview.chromium.org/52653005

git-svn-id: svn://svn.chromium.org/blink/trunk@161300 bbb929c8-8fbe-4397-9dbb-9b2b20218538