The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f6ac68b04228683aa3176ad4020e109fbde5abf6

commit f6ac68b04228683aa3176ad4020e109fbde5abf6
Author: karandeepb <karandeepb@chromium.org>
Date: Mon Sep 12 01:42:45 2016

MacViews: Fix flashing of opaque non-modal windows on display.

Currently, opaque non-modal windows like the Task Manager appear with a "flash",
when displayed initially. This is because if the frame from the compositor
hasn't arrived yet, the background color of the window shows through. When the
frame arrives, the actual contents are displayed, causing a "flash".

To get around this, for opaque non-modal windows, set the alpha value of the
window to 0, till the correct frame from the compositor is received. Also,
ignore mouse clicks till then. This also fixes the "black strip" that is
displayed in the non webcontents area of the MacViewsBrowser, when it is
displayed initially.

BUG= 623950 ,  645343 
TEST=With chrome://flags/#mac-views-native-dialogs enabled, open the Task
Manager. Observe it is not displayed with a Flash. (Record a screencast and
observe frame by frame).
TEST=Build with mac_views_browser=true. Open the browser and observe no black
strip is displayed in the non web-contents area, when it is displayed initially.

Review-Url: https://codereview.chromium.org/2312133002
Cr-Commit-Position: refs/heads/master@{#417863}

[modify] https://crrev.com/f6ac68b04228683aa3176ad4020e109fbde5abf6/ui/views/cocoa/bridged_native_widget.h
[modify] https://crrev.com/f6ac68b04228683aa3176ad4020e109fbde5abf6/ui/views/cocoa/bridged_native_widget.mm

karandeepb: is this fixed now? It sounds from #1 like it is.

Think it should be. Not sure why I didn't mark it as Fixed. Would be good to verify before closing the bug.

Oh ok. c#3 answers that. While #1 fixed the black strip during opening the browser, closing the browser still caused the black strip. 

IIRC, I had summarized the reason on one of the flashing window bugs. The reason IIRC was that we were destroying the compositor incorrectly. But it should be fixable.

See https://bugs.chromium.org/p/chromium/issues/detail?id=649354#c4 which I think may also fix this.

[Bulk Edit]
Applying M-68 milestone per email discussion with ellyjones@. Pls change it if milestone is incorrectly applied. 

MacViews triage: can't reproduce this any more, WontFix :)