Propagate Options via ValueForCustomProperty.

This Options object will soon need to carry information that
ValueForCustomProperty needs to act upon. Specifically, it
needs to know whether the resolved CSSVariableData should be
stored on the ComputedStyle before returning.

Also, since the Options object is now available here, let
ValueForCustomProperty return nullptr if a variable is disallowed.
This avoids an extra PropertyRegistation lookup at one of the
callsites.

R=futhark@chromium.org

Bug: 641877
Change-Id: I85f51ff23d23ab404f6fc133e2017f70dd5aea03
Reviewed-on: https://chromium-review.googlesource.com/1235721
Commit-Queue: Anders Ruud <andruud@chromium.org>
Reviewed-by: Rune Lillesveen <futhark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#592787}
2 files changed