Implement 'will-change' parsing

Implement 'will-change' parsing

This implements parsing for the 'will-change' CSS
property. This property is protected by a runtime
flag.

Intent-to-implement:
https://groups.google.com/a/chromium.org/forum/#!topic/blink-dev/M62y2nKZ-gE

Spec: http://tabatkins.github.io/specs/css-will-change/

BUG=313532
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=167394

[eseidel, 2014-02-18 23:33:52]

lgtm

https://codereview.chromium.org/167603002/diff/180001/Source/core/rendering/s...
File Source/core/rendering/style/RenderStyle.h (right):

https://codereview.chromium.org/167603002/diff/180001/Source/core/rendering/s...
Source/core/rendering/style/RenderStyle.h:1383: void
setWillChangeProperties(const Vector<CSSPropertyID>& properties) {
SET_VAR(rareNonInheritedData.access()->m_willChange, m_properties, properties);
}
We'll end up copying the vector here.  That's not necessarily bad, but if
rareNonInheritedData isn't sufficiently rare, this could show up on profiles.

[ajuma, 2014-02-19 00:12:46]

The CQ bit was checked by ajuma@chromium.org

[commit-bot: I haz the power, 2014-02-19 00:12:57]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/ajuma@chromium.org/167603002/180001

[commit-bot: I haz the power, 2014-02-19 03:22:12]

Change committed as 167394