GitLab

Add a "use-default-poster" CSS class and add it if the video
element does not have a video frame or poster to display. As
per the spec then hide the controls apart from the play button
and display a gradient background.

BUG=761308

Change-Id: I579a1be27ecdb375e770b2fbc841593f7ce2abc3
Reviewed-on: https://chromium-review.googlesource.com/733092
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#512884}