[BlinkGenPropertyTrees] Initiailize double_sided of synthetic effect

Previously synthetic effects always had double_sided==false, causing
the layer disappear when the backface was facing forward.

Bug: 928190
Change-Id: I35534b40346d5c5918bc99c00a4ca6b4e3b68796
Reviewed-on: https://chromium-review.googlesource.com/c/1475815
Reviewed-by: Philip Rogers <pdr@chromium.org>
Commit-Queue: Xianzhu Wang <wangxianzhu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#632764}
3 files changed