The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/611bc1e28e9131c6bc94b931cf48d1e770290f45

commit 611bc1e28e9131c6bc94b931cf48d1e770290f45
Author: spqchan <spqchan@chromium.org>
Date: Tue Oct 24 17:43:12 2017

[Mac] Lock the Fullscreen Toolbar Visibility

Currently if the Fullscreen Toolbar's style is set
to "hidden", TopChrome will hide, even if keyboard
access or Voice Over is focused on one of its views.

This creates a challenge for accessibility users
who are trying to navigate TopChrome. To fix this
issue, BrowserWindowController will lock the
fullscreen's toolbar visibility in fullscreen if
one of TopChrome's view gains first responder
status.

Bug:  775124 
Change-Id: I14ba02eaa1410e8f9096540bf5c7935cacd2c402
Reviewed-on: https://chromium-review.googlesource.com/728417
Commit-Queue: Sarah Chan <spqchan@chromium.org>
Reviewed-by: Elly Fong-Jones <ellyjones@chromium.org>
Cr-Commit-Position: refs/heads/master@{#511201}
[modify] https://crrev.com/611bc1e28e9131c6bc94b931cf48d1e770290f45/chrome/browser/ui/cocoa/browser_window_controller.h
[modify] https://crrev.com/611bc1e28e9131c6bc94b931cf48d1e770290f45/chrome/browser/ui/cocoa/browser_window_controller.mm
[modify] https://crrev.com/611bc1e28e9131c6bc94b931cf48d1e770290f45/chrome/browser/ui/cocoa/browser_window_controller_private.mm
[modify] https://crrev.com/611bc1e28e9131c6bc94b931cf48d1e770290f45/chrome/browser/ui/cocoa/framed_browser_window.mm
[modify] https://crrev.com/611bc1e28e9131c6bc94b931cf48d1e770290f45/chrome/browser/ui/cocoa/fullscreen/fullscreen_toolbar_controller.h
[modify] https://crrev.com/611bc1e28e9131c6bc94b931cf48d1e770290f45/chrome/browser/ui/cocoa/fullscreen/fullscreen_toolbar_controller.mm

Tested the issue in MacBook Pro (Retina, 15-inch, Mid 2014), 10.12.6 using chrome version #64.0.3249.0 as per the steps in the URL:: https://docs.google.com/document/d/1kY-99Uy3Kkswe5A-0krX0G3mOldD9Uc2iokR9IQ2eMY/edit# from issue id: 772947.

Following are the steps followed to reproduce the issue.
------------
1. Navigated to chrome://flags and enabled #enable-fullscreen-toolbar-reveal.
2. Opened the View menu and unchecked “Always Show Toolbar in Full Screen” option.
3. Selected “Enter Full Screen” from the View menu.
4. Turned the voice over on using Cmd+F5.
5. Navigated to a www.yahoo.com and opened a link in another tab.
6. Used Cmd-Option-Right Arrow to switch to the new tab.
7. Observed that fullscreen toolbar disappeared when voiceOver was interacting with it. This is not as expected.

Attached a screen cast for reference.

spqchan@ - Could you please verify the attached screen cast and please confirm the expected behaviour and the fix.

Thanks...!!

Deleted: 775124.mp4 8.7 MB

	775124.mp4 8.7 MB View Download

Ah yes, sorry, that is the incorrect verification step.
VoiceOver isn't actually focused on the toolbar.

To reproduce:
1. Navigated to chrome://flags and enabled #enable-fullscreen-toolbar-reveal.
2. Opened the View menu and unchecked “Always Show Toolbar in Full Screen” option.
3. Selected “Enter Full Screen” from the View menu.
4. Turned the voice over on using Cmd+F5.
5. Press tab until VoiceOver start to focus on the items on the toolbar. The toolbar should drop down when one of its items is focused

+lpalmaro

Hey lpalmaro! The change is now available in Canary. If you have the time, can you play around and give me your thoughts on it? Thanks!