Apply custom properties in user style sheets

With crrev.com/c/641294 we introduced user style sheets, but without taking
into account custom properties. This patch adds support for custom properties
in user style sheets by calling StyleResolver::ApplyMatchedProperties for user
rules in the correct order.

BUG=632009,781223

Change-Id: I1c103fc37484835008b1b55e9b3b8099af50a48a
Reviewed-on: https://chromium-review.googlesource.com/754247
Reviewed-by: nainar <nainar@chromium.org>
Commit-Queue: nainar <nainar@chromium.org>
Cr-Commit-Position: refs/heads/master@{#515478}
2 files changed