The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/4c48422d79696901578dd987aee50ee8dbe87e2e

commit 4c48422d79696901578dd987aee50ee8dbe87e2e
Author: Luciano Pacheco <lucmult@chromium.org>
Date: Tue Nov 20 10:03:48 2018

Quick view: allow tab to audio and video controls

Change quick view for audios and videos to allow to use tab to focus
the audio and video HTML5 tag's controls, e.g.: play, slider and
volume.

Add a blue outline for focused elements inside audio and video HTML5
tags, as part of the accessibility to make visually clear what control
is focused.

Change audio to not show the download button since it's already in the
file system and downloading doesn't make sense in that context.

Change video to not show picture-in-picture since it doesn't work for
quick-view.

Bug: 627701,  801522 ,  848216 
Change-Id: Ie46159bc90d2948bbac98d69acaf8b53e62d5e58
Reviewed-on: https://chromium-review.googlesource.com/c/1341777
Commit-Queue: Luciano Pacheco <lucmult@chromium.org>
Reviewed-by: Sam McNally <sammc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#609653}
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/foreground/elements/files_quick_view.html
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/foreground/elements/files_safe_audio_webview_content.css
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/foreground/elements/files_safe_audio_webview_content.html
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/foreground/elements/files_safe_media.js
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/foreground/elements/files_safe_video_webview_content.css
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/foreground/elements/files_safe_video_webview_content.html
[modify] https://crrev.com/4c48422d79696901578dd987aee50ee8dbe87e2e/ui/file_manager/file_manager/main.html

Ops, I closed the wrong bug. :-/