Add openQuickViewBackgroundColorHtml test

Untrusted content (HTML here) is rendered in Quick View in a <webview>
element. Its parent <file-safe-media> sets the background color of the
rendered HTML and that color must be solid white. Test that.

Bug: 891150
Change-Id: I10975df3e862b4d8746c97adc43aaf18b248dd4b
Reviewed-on: https://chromium-review.googlesource.com/c/1258670
Reviewed-by: Sam McNally <sammc@chromium.org>
Commit-Queue: Noel Gordon <noel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#596183}
2 files changed