CSS: Handle ::part rules when building RuleSets.

Add a part_pseudo_rules vector to RuleSet to hold rules with ::part
selectors and update RuleSet::FindBestRuleSetAndAdd to populate this.


Bug: 805271
Change-Id: If18cabbd8c933f49a252e2f659246cb0e0471e3f
Reviewed-on: https://chromium-review.googlesource.com/972766
Commit-Queue: Fergal Daly <fergal@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#544969}
2 files changed