Previously it was looking at draw_transform which doesn't get filled in
on the main thread by property trees.
Once main thread CDP is removed, Layer::draw_transform can do this work,
and this can be reverted.
R=weiliangc@chromium.org
BUG=502041
CQ_INCLUDE_TRYBOTS=tryserver.blink:linux_blink_rel
Review URL: https://codereview.chromium.org/1295203002
Cr-Commit-Position: refs/heads/master@{#343802}
f6903539e8