Allow setting runtime-enabled features from a string.

Allow setting runtime-enabled features from a string.

This provides the plumbing necessary for content/ to provide flags to
generally enable and disable simple runtime-enabled features. Some features
will still require more complicated logic, but this should make the 90%
case easier.

The Chromium-side CL is:
  https://codereview.chromium.org/898483004/

BUG=454504
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=189510

[jbroman, 2015-02-02 21:25:40]

jbroman@chromium.org changed reviewers:
+ chrishtr@chromium.org, pdr@chromium.org

[jbroman, 2015-02-02 21:25:40]

If this LGTY, I'll send the Chromium-side CL for review.

Ultimately, things that need Chromium support (if cc needs to change its
behaviour explicitly based on the flag) will still need separate switches. But
for simple features, or features still early in development, I think this will
often suffice.

And it beats adding/removing status=stable from RuntimeEnabledFeatures.in
repeatedly.

[chrishtr, 2015-02-02 21:36:01]

lgtm

[jbroman, 2015-02-02 21:44:28]

On 2015/02/02 21:36:01, chrishtr wrote:
> lgtm

waiting for approval on chromium CL before landing

[pdr., 2015-02-02 22:27:28]

pdr@chromium.org changed reviewers:
+ eseidel@chromium.org

[pdr., 2015-02-02 22:27:44]

This is cool! +eseidel just FYI :)

[jbroman, 2015-02-04 15:03:01]

The CQ bit was checked by jbroman@chromium.org

[commit-bot: I haz the power, 2015-02-04 15:04:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/890723004/1

[commit-bot: I haz the power, 2015-02-04 16:03:29]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=189510