Add fullscreen container behavior.

Set the VK Aura Window to be transparent.
Otherwise WindowOcclusionTracker will set the Web Page Aura Window state
to be occluded and user can not see the committed input texts after VK
turns fullscreen. See conditions defined in VisibleWindowIsOpaque.

Bug: 826617
Change-Id: Idd8c525f205e608fe53fb59f85d302175b7a6246
Reviewed-on: https://chromium-review.googlesource.com/1023380
Commit-Queue: Jianzhou Feng <jzfeng@chromium.org>
Reviewed-by: Toni Barzic <tbarzic@chromium.org>
Reviewed-by: Yuichiro Hanada <yhanada@chromium.org>
Cr-Commit-Position: refs/heads/master@{#552995}
8 files changed