Update timeline-set-current-time to test setting animation timelines instead of document timelines

Unfortunately, we do not yet implement DocumentTimeline, so this test
fails.

Relevant spec:
http://w3c.github.io/web-animations/#the-current-time-of-an-animation

BUG=623437

Review-Url: https://codereview.chromium.org/2138303002
Cr-Commit-Position: refs/heads/master@{#405016}
5 files changed