You are probably looking for a change made after 443240 (known good), but no later than 443241 (first known bad).

CHANGELOG URL:

https://chromium.googlesource.com/chromium/src/+log/b103d6c66bbd7bebfe22affab2ea4930685a55bc..972a4d1ae26576f2a0cee1066a6ded6616538641

Suspect: https://chromium.googlesource.com/chromium/src/+/972a4d1ae26576f2a0cee1066a6ded6616538641

Mihai, this seems like it might be a more general problem with modal dialogues?

Either way, certainly not P1.

Sync confirmation dialog is a browser window modal dialog. I am re-assigning this bug to the owners of components/constrained_window/ as this is a generic browser-modal issue.

Jérôme, this bisected to your change. Why did you reassign?

I moved it to msarda since he is in charge of that now.

Jerome changed the sync confirmation dialog to be a browser modal dialog instead of a tab modal dialog (the fact that it was a tab modal dialog in the past was a bug as the lifecycle of the sync confirmation dialog is not related to the tab at all).
The sync confirmation dialog is a regular browser modal dialog (it does not do anything special in terms of display). So, like any other browser modal dialog, the sync modal dialog blocks the user from interacting with the browser window.

I reassigned the bug to the owners of components/constrained_window/ as this bug is a generic bug of the Tools menu button being enabled when a browser modal dialog is presented on top of the browser window.

--Chrome Identity automated triaging--

This bug is Assigned and has gone one month without any activity, so it is being moved to Available to indicate that it is not actively being worked on. If you are working on this bug, please mark yourself as the owner and move back to Assigned. Please see https://goo.gl/78kbny for more details. Please remove the Services>SignIn or UI>Browser>Profiles components if this bug isn't related to Chrome Identity.

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

--Chrome Identity automated triaging--

This bug is Assigned and has gone one month without any activity, so it is being moved to Available to indicate that it is not actively being worked on. If you are working on this bug, please mark yourself as the owner and move back to Assigned. Please see https://goo.gl/78kbny for more details. Please remove the Services>SignIn or UI>Browser>Profiles components if this bug isn't related to Chrome Identity.

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

***Mass UI Triage***

Just to update:

Still able to reproduce this bug on Mac(10.13.1, 10.13.6, 10.14.2) OS using Latest canary #72.0.36010.2 

@wittman: Could you please take look into it.

Thank you.

I am unlikely to get to this anytime soon. Downgrading priority and unassigning myself.