Enable support for CSS Conditional Rules

Enable support for CSS Conditional Rules

This patch removes the ENABLE_CSS3_CONDITIONAL_RULES compile time flag,
and thus brings support for CSS Conditional Rules to Chromium.

Three tests have been contributed by the author of this feature,
Pablof Flouret <pablof@motorola.com>;, all of which pass. In order to get
there, I had to slightly update the CSSGrammar.y.in file to properly
identify "!important" as a failing rule. Three warnings in that same
file have also been resolved.

Shipping CSS Conditional Rules received an LGTM from Eric Seidel on April
15th, 2013, both un-prefixed and unguarded.

BUG=227103
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=148817

[Peter Beverloo, 2013-04-05 20:03:47]

Ojan, is this something you could take a look at?  We can hold off landing this
until the initial dust settles either way.

* This feature is not prefixed, and introduces the CSS @supports at-rule to the
platform, as well as the "window.CSS.supports()" method.
* There is no way to disable parsing of CSS at runtime right now. Disabling the
"window.CSS.supports()" method but not parsing seems a bit odd. An option would
be to always pass the check if it can't be interpret.

[esprehn, 2013-04-05 20:36:07]

Please wait for the API review before landing this. :)

Ideally we need a way for runtime flags to control the existence of the JS API.

[ojan, 2013-04-16 23:21:42]

lgtm

Looks like there were no objections in the API review. 

Just to double-check, this doesn't expose any new vendor-prefixed APIs, right?

[Peter Beverloo, 2013-04-16 23:28:43]

On 2013/04/16 23:21:42, ojan wrote:
> Just to double-check, this doesn't expose any new vendor-prefixed APIs, right?

Correct.  Thank you for the review, I'll rebase, re-test and land this tomorrow.

[commit-bot: I haz the power, 2013-04-22 11:48:03]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/peter@chromium.org/13646013/5001

[commit-bot: I haz the power, 2013-04-22 11:48:11]

Presubmit check for 13646013-5001 failed and returned exit status 1.

INFO:root:Found 23 file(s).
Running presubmit commit checks ...
Running /b/commit-queue/workdir/blink/PRESUBMIT.py

** Presubmit ERRORS **
Missing LGTM from an OWNER for these files:
    Source/WebKit/chromium/features.gypi
    Source/bindings/v8/custom/V8CSSRuleCustom.cpp

Presubmit checks took 2.8s to calculate.

[jochen (gone - plz use gerrit), 2013-04-22 12:49:36]

LGTM

Mind to ping the blink-dev thread again after this has landed?

[Peter Beverloo, 2013-04-22 13:06:37]

On 2013/04/22 12:49:36, jochen wrote:
> LGTM
> 
> Mind to ping the blink-dev thread again after this has landed?

Of course. Thanks!

[commit-bot: I haz the power, 2013-04-22 13:13:04]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/peter@chromium.org/13646013/5001

[commit-bot: I haz the power, 2013-04-22 13:47:30]

Change committed as 148817