Build javascript unit tests with gn.

Build javascript unit tests with gn.

This extends the js2gtest template and uses it for the gtestjs
unit tests.

BUG=None

Committed: https://crrev.com/fa69ff87b07d19f36468412313fab80f4e3b389d
Cr-Commit-Position: refs/heads/master@{#330907}

[Peter Lundblad, 2015-05-20 13:09:19]

plundblad@chromium.org changed reviewers:
+ brettw@chromium.org

[brettw, 2015-05-20 18:28:48]

lgtm

[Peter Lundblad, 2015-05-21 06:54:12]

The CQ bit was checked by plundblad@chromium.org

[commit-bot: I haz the power, 2015-05-21 06:54:21]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1145113002/1

[commit-bot: I haz the power, 2015-05-21 07:01:24]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-05-21 07:02:17]

Patchset 1 (id:??) landed as
https://crrev.com/fa69ff87b07d19f36468412313fab80f4e3b389d
Cr-Commit-Position: refs/heads/master@{#330907}