Add Quick View load test for a Linux files volume

Cargo-cult the MTP / USB test cases: mount Linux files (Crostini), and
open one of its files in QuickView.

QuickView involves <webview>, as we have seen in this bug. <webview>'s
are only available to chrome extensions and hence we should use a test
system that supports extensions to cover <webview> use.

Bug: 891150
Change-Id: I7fe3814c89125f5c06d4465726fa0cbe851a1659
Reviewed-on: https://chromium-review.googlesource.com/c/1270202
Commit-Queue: Noel Gordon <noel@chromium.org>
Reviewed-by: Luciano Pacheco <lucmult@chromium.org>
Cr-Commit-Position: refs/heads/master@{#597794}
2 files changed