CSS Parser: Mark on stylesheets whether the first rule was valid

CSS Parser: Mark on stylesheets whether the first rule was valid

This makes the new CSS parser call setHasSyntacticallyValidCSSHeader so
that we can determine whether we should allow stylesheets to be used.
A StyleRuleCharset class is added so that we can properly signal whether
a rule was valid (now consumeAtRule and consumeQualifiedRule will return
nullptr exactly when the rule is valid). For more context, the logic
regarding disallowing certain stylesheets is discussed in bug 9877.

BUG=330389
Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=192339

[Timothy Loh, 2015-03-19 07:15:49]

timloh@chromium.org changed reviewers:
+ alancutter@chromium.org, dstockwell@chromium.org

[dstockwell, 2015-03-22 23:14:35]

lgtm

[Timothy Loh, 2015-03-22 23:19:51]

The CQ bit was checked by timloh@chromium.org

[commit-bot: I haz the power, 2015-03-22 23:20:00]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1018213004/40001

[commit-bot: I haz the power, 2015-03-23 00:59:01]

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

[commit-bot: I haz the power, 2015-03-23 00:59:02]

Try jobs failed on following builders:
  linux_blink_rel on tryserver.blink (JOB_FAILED,
http://build.chromium.org/p/tryserver.blink/builders/linux_blink_rel/builds/5...)

[Timothy Loh, 2015-03-23 08:24:57]

The CQ bit was checked by timloh@chromium.org

[commit-bot: I haz the power, 2015-03-23 08:25:16]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1018213004/40001

[commit-bot: I haz the power, 2015-03-23 09:31:25]

Committed patchset #3 (id:40001) as
https://src.chromium.org/viewvc/blink?view=rev&revision=192339