webkit: Use subprocess.check_output

webkit: Use subprocess.check_output

Fixes "FIXME" and makes this file Python 2.7 only.

BUG=666161

[mithro, 2016-11-22 03:55:34]

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

[mithro, 2016-11-22 03:55:34]

Is there anyone still using anything earlier than Python 2.7!?

[Timothy Loh, 2016-11-23 00:29:43]

lgtm but update make_css_value_keywords.py too where this is copy-pasted

On 2016/11/22 03:55:34, mithro wrote:
> Is there anyone still using anything earlier than Python 2.7!?

Probably not since code search has lots more hits for check_output

[mithro, 2016-11-30 06:33:20]

The CQ bit was checked by tansell@chromium.org

[mithro, 2016-11-30 06:34:08]

The CQ bit was unchecked by tansell@chromium.org

[commit-bot: I haz the power, 2016-11-30 06:34:17]

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

[commit-bot: I haz the power, 2016-11-30 06:34:20]

This CL has an open dependency (Issue 2521893002 Patch 20001). Please resolve
the dependency and try again.
If you are sure that there is no real dependency, please use one of the options
listed in https://goo.gl/9Es4OR to land the CL.

[mithro, 2017-01-31 01:31:37]

The CQ bit was checked by tansell@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-01-31 01:31:58]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-31 01:44:53]

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

[commit-bot: I haz the power, 2017-01-31 01:44:54]

Dry run: Try jobs failed on following builders:
  chromeos_amd64-generic_chromium_compile_only_ng on
master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/chromeos_amd64-...)
  linux_chromium_tsan_rel_ng on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[mithro, 2017-01-31 17:30:04]

The CQ bit was checked by tansell@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-01-31 17:30:43]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-01-31 17:40:26]

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

[commit-bot: I haz the power, 2017-01-31 17:40:27]

Dry run: Try jobs failed on following builders:
  cast_shell_linux on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/cast_shell_linu...)
  linux_chromium_tsan_rel_ng on master.tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)