[test] Run webkit tests as part of default testing on the bots.

[test] Run webkit tests as part of default testing on the bots.

The test suite is ran in 60% of the bots anyway and the
step is very short. For swarming, it's better to run this
together in one step as each step triggers a different bot.

BUG=chromium:535160
LOG=n
NOTRY=true

Committed: https://crrev.com/c8f7583a48c8391f3a3620bafd20537f1a2d55a5
Cr-Commit-Position: refs/heads/master@{#31360}

[Michael Achenbach, 2015-10-19 08:08:26]

machenbach@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Michael Achenbach, 2015-10-19 08:08:33]

PTAL

[Jakob Kummerow, 2015-10-19 08:53:14]

LGTM.

For the record: we discussed simply adding webkit tests to the default set, but
agreed that it wasn't clear whether the increase in default coverage was worth
the ~10% or so of additional test execution time it would cost. Running those
tests manually is still easy.

[Michael Achenbach, 2015-10-19 08:53:37]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-10-19 08:53:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1413023002/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1413023002/1

[commit-bot: I haz the power, 2015-10-19 08:54:58]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-19 08:55:18]

Patchset 1 (id:??) landed as
https://crrev.com/c8f7583a48c8391f3a3620bafd20537f1a2d55a5
Cr-Commit-Position: refs/heads/master@{#31360}