Autogenerate lists of "stable", "experimental" and "test" features from RuntimeEnabledFeatures.in

This completes the transition of moving control over the set of "stable" features from Content down into Blink and making it autogenerated.

I also needed to add value-validation to InFile parsing for this change.

There is still more we could autogenerate here, but this covers most use-cases for contributors wanting to add experimental features to the tree and be able to easily turn them on/off.  (And for API OWNERS being able to tell what we're actually shipping as part of the "stable" API.)

I suspect we'll want to iterate on this file format further, once we've had some time to try it.  I expect that many other systems may want to read this file (including possibly layout tests and the chrome feature status dashboard).

We may want to change the default to be "test" instead of "off" as most "off" features actually end up enabled in some part of the product through other (non-standard or deprecated) ways up in Content.

I will announce this on Blink dev once it's successfully integrated into the tree.

BUG=237740
R=abarth@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=149923

[eseidel, 2013-05-07 23:28:29]

ptal

[abarth-chromium, 2013-05-07 23:33:07]

lgtm

[eseidel, 2013-05-08 01:13:15]

Committed patchset #2 manually as r149923 (presubmit successful).