Enable new multicol for testing and experimental web platform features.

Enable new multicol for testing and experimental web platform features.

This is a re-land of https://codereview.chromium.org/1028383002

There's already a RuntimeEnabledFeatures flag for region based
(aka. "new") multicol. So far it's only been used to toggle support
for column-fill (only supported in the new implementation), but will
from now on be used to determine whether to use the region based
implementation or not.

Remove internals.settings.setRegionBasedColumnsEnabled().

We need to keep a method for region based multicol (that does nothing)
in WebSettings for now, since it's still being called from the
Chromium side. Will be cleaned up later, when the
--enable-region-based-columns command line flag (which from now on has
no effect) is gone. See crbug.com/350853

Remove virtual/regionbasedcolumns tests, since region based multicol
is what's tested by default from now on. At the same time, add
virtual/stable/ tests, so that we still get test coverage for the old
implementation, since that's still what's shipping. This move causes
many changes in TestExpectations. All multicol test expectations that
used to be foo/* will now be virtual/stable/foo/* , and everything
that used to be virtual/regionbased/foo/* is now foo/* .

svg/text/columns-do-not-apply.html now passes again.

A few test expectations also need to be updated:

fast/dom/Element/getBoundingClientRect.html: Regenerated expectation
file. New multicol has improved column balancing, resulting in 6px
shorter columns.

fast/borders/border-antialiasing.html: Schedule for
rebaseline. Clipping improvements in new multicol.

fast/repaint/multicol-as-paint-container.html: Schedule for
rebaseline. Different individual rectangles, but same resulting
rectangle.

fast/repaint/multicol-repaint.html: Schedule for rebaseline. Clipping
improvements in new multicol.

BUG=334335, 467468
R=dsinclair@chromium.org,jchaffraix@chromium.org,kbr@chromium.org

Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=194883

[dsinclair, 2015-05-04 13:39:34]

lgtm

[mstensho (USE GERRIT), 2015-05-04 16:11:28]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-05-04 16:11:57]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1119293002/1

[commit-bot: I haz the power, 2015-05-04 16:24:11]

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

[commit-bot: I haz the power, 2015-05-04 16:24:13]

Try jobs failed on following builders:
  blink_presubmit on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/blink_presubmit/builds/3...)

[mstensho (USE GERRIT), 2015-05-04 16:51:42]

Oops. Need moar Igtm. kbr?

[chrishtr, 2015-05-04 16:58:46]

chrishtr@chromium.org changed reviewers:
+ chrishtr@chromium.org

[chrishtr, 2015-05-04 16:58:48]

lgtm

[Ken Russell (switch to Gerrit), 2015-05-04 17:15:27]

Source/web LGTM

[mstensho (USE GERRIT), 2015-05-04 18:34:18]

The CQ bit was checked by mstensho@opera.com

[commit-bot: I haz the power, 2015-05-04 18:34:34]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1119293002/1

[commit-bot: I haz the power, 2015-05-04 18:47:21]

Committed patchset #1 (id:1) as
https://src.chromium.org/viewvc/blink?view=rev&revision=194883