Add Quick View video load test

Now we have the QuickView <webview> infra to detect the 'loaded' state
of thew <webview> content, add a <file-safe-media> video test and also
check the <webview> renders its content on a transparent black body.

Bug: 891150
Change-Id: I634a60ba733bfff79ed72b0e75d7024da4c8182c
Reviewed-on: https://chromium-review.googlesource.com/c/1264097
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597028}
2 files changed