I patched for this issue.

See https://chromium-review.googlesource.com/c/chromium/src/+/1345694

This patch is landed. (https://chromium-review.googlesource.com/c/chromium/src/+/1345694)

Unable to reproduce the issue on reported chrome version 72.0.3616.0 and latest chrome 72.0.3618.0 using Windows 10. Attaching screencast for reference.
Steps: 
---------
1. Launched reported chrome 
2. Enabled "back" button or "forward" button
3. Long pressed back button and forward button.
3. Closed drop down menu by clicking o other space
As we have observed that the button will be normal.

@Reporter: Could you please review the attached screen-cast and confirm if anything being missed here and help in verifying the fix.

Thanks.!

Deleted: 907358.mp4 1.9 MB

	907358.mp4 1.9 MB View Download

Show dropdownmenu using long press or right click at least twice and closing menu.
The issue isn't occurred in 72.0.3618.0. Because my patch is landed.(the issue was occurred in 72.0.3616.0)

Chrome(70.0.3538.102), not canary, is still occurred.

Deleted: backbutton_issue.mp4 463 KB

	backbutton_issue.mp4 463 KB View Download

Thank you for providing more feedback. Adding the requester to the cc list.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

Able to reproduce issue on reported chrome version 72.0.3616.0 and issue not seen on latest chrome 72.0.3622.0 using Windows 10 and Mac 10.14.0. Hence providing reverse bisect information below.

Note: Issue not observed on Ubuntu 
Bisect Info:
================
Good build: 72.0.3618.0
Bad build:  72.0.3617.0

CHANGELOG URL:
You are probably looking for a change made after 610074 (known good), but no later than 610075 (first known bad).
https://chromium.googlesource.com/chromium/src/+log/90928aa9832fccb05719e752afa6835b24b1f1d7..99191ddaa39d7bd3c1ee8296a85616aa9b3210f6
suspect: https://chromium.googlesource.com/chromium/src/+/99191ddaa39d7bd3c1ee8296a85616aa9b3210f6
Reviewed-on: https://chromium-review.googlesource.com/c/1345694

Elly Fong-Jones@: Please confirm the issue and help in re-assigning if it is not related to your change. Adding RBS label for M-71 feel free to change it if not required.

Note: Owner's mail id is available to assign. Hence assigning to reviewer (ellyjones@chromium.org)

Thanks..!

This is Fixed per #4.

[Auto-generated comment by a script] We noticed that this issue is targeted for M-70; 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-70 label, otherwise remove Merge-TBD label. Thanks.

No merge.

Removing "Merge-TBD" label per comment #11.