Sync GN unit tests with GYP, add checking script.

Sync GN unit tests with GYP, add checking script.

Some of these JavaScript gtest tests were missing from the GN build because
they needed to go into a special target.

The included script will find and print out lists of test differences.

Reland of https://codereview.chromium.org/1289423004/ with data added to the js2gtest template so it works in swarming.

TBR=jam
BUG=521944

[brettw, 2015-08-18 20:11:48]

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

[brettw, 2015-08-18 20:12:37]

The CQ bit was checked by brettw@chromium.org

[commit-bot: I haz the power, 2015-08-18 20:13:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1296363005/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1296363005/20001

[commit-bot: I haz the power, 2015-08-18 21:35:44]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-08-18 21:35:45]

Try jobs failed on following builders:
  win_chromium_rel_ng on tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[brettw, 2015-08-18 21:41:09]

Committed patchset #2 (id:20001) to pending queue manually as
c1b38c56146838ff3e73757595672714b389018f (presubmit successful).