Confirmed and narrowed down the bisect range using both x64 and x86 snapshots:
  466205 (good) - 466207 (bad), 60.0.3077.0
  https://chromium.googlesource.com/chromium/src/+log/19d202db..fec5a00d?pretty=fuller
  Suspecting the same CL r466207 "Remove use of WS_EX_COMPOSITED for translucent windows"

==================================

It should be noted that the awkwardly stuttering animation of the popup height started earlier.
Should I submit this in a new bug report?
  457623 (good) - 457637 (bad), 59.0.3044.0
  https://chromium.googlesource.com/chromium/src/+log/4d824f56..9fa493ef?pretty=fuller
  Suspecting r457632 "DCLayerOverlay should damage entire frame on resize"
  Suspecting r457630 "cc: Use SkCreateColorSpaceXformCanvas for color transforms"

Also marking RBS for M60 at least and cc'ing M59 TPM in case this is deemed serious enough for M59.

I've got a patch that seems to fix it for me at https://chromium-review.googlesource.com/564147 , though I'm not sure precisely why that patch helps. I'm not sure this is quite serious enough for ReleaseBlock-Stable, and I really doubt we'd want to merge a fix to M59.

Able to reproduce the issue on Win-10 using latest canary #61.0.3155.0 and latest beta #60.0.3112.50.

Attached a screen cast for reference.

jbauman@ - Could you please verify the screen cast and please confirm the behavior.

Thanks...!!

Deleted: 739724.mp4 1.2 MB

	739724.mp4 1.2 MB View Download

I don't think that screencast reproduces the black square behavior - it shows a little square in the corner, but it's colored mostly white. I think this bug will only happen on Windows 10 if you use the --disable-d3d11 command-line flag. On windows 8.1, 8, and 7 this bug should always happen even without that flag. 

Reg c#6:

I do not think we have one more M59 stable release. Would be great if we can merge this fix to M60 (branch# 3112) if it is safe, so that eventually be the next Stable candidate.

Thank you!

I looked at the CL are we confident this won't result in flicker for users?  Since this bug takes some work to run into to (clicking rapidly on the extension action icon) I'm leaning towards waiting until M61 so it can bake for a while on Dev/Beta.

#12, no, every or almost every click on every extension icon produces the ugly black rectangle. The bug is really bad. 

The original report mentioned repetitive clicking only to facilitate certain reproduction of the bug. 

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/64dd9570929e2427dbd76cc6ccc30892fa849f4b

commit 64dd9570929e2427dbd76cc6ccc30892fa849f4b
Author: John Bauman <jbauman@chromium.org>
Date: Wed Jul 19 20:40:51 2017

Set SWP_NOCOPYBITS when resizing translucent windows.

This seems to fix the black flashing that was happening with the
extension popup UI. WS_EX_COMPOSITED was originally hiding this issue in
most cases (except possibly  http://crbug.com/586454  ), possibly because
it didn't allow GDI painting outside of WM_PAINT (like is happening here).

Bug:  739724 
Change-Id: I897deedb3bf7f2c2ff799cb24a98e0f94f835ea9
Reviewed-on: https://chromium-review.googlesource.com/564147
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Ananta Iyengar <ananta@chromium.org>
Commit-Queue: John Bauman <jbauman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#487963}
[modify] https://crrev.com/64dd9570929e2427dbd76cc6ccc30892fa849f4b/ui/views/win/hwnd_message_handler.cc

This is fixed in M61, but I think the fix is too risky (may possibly cause flickering windows) to merge to M60.

[Auto-generated comment by a script] We noticed that this issue is targeted for M-60; it appears the fix may have landed after branch point, meaning a merge might be required. Please confirm if a merge is required here - if so add Merge-Request-60 label, otherwise remove Merge-TBD label. Thanks.