Stabilize transition testcase.

Stabilize transition testcase.

Roughly 1% of the times transitions/svg-visited-link-transitions.html
runs it will set the "active" class before a previous layout. When that
happens there won't be any style to animate so the elements reach the
final step immediately.

Fixed by forcing a layout pass before setting the "active" style.

BUG=450497
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=189106

[Daniel Bratell, 2015-01-27 15:26:33]

bratell@opera.com changed reviewers:
+ alancutter@chromium.org

[Daniel Bratell, 2015-01-27 15:26:34]

alancutter, can you please take a look?

[Timothy Loh, 2015-01-28 00:52:08]

timloh@chromium.org changed reviewers:
+ timloh@chromium.org

[Timothy Loh, 2015-01-28 00:52:08]

lgtm

[Daniel Bratell, 2015-01-28 10:02:35]

The CQ bit was checked by bratell@opera.com

[commit-bot: I haz the power, 2015-01-28 10:02:49]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/876343002/1

[commit-bot: I haz the power, 2015-01-28 12:32:48]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=189106