(If the CL from comment 0 is unrelated, maybe https://chromium.googlesource.com/chromium/src/+/09f8bdbd7d6228963e1ab3566bd9caab1c23731f may also be a candidate.)

My CL should only have affected BrowserAppMenuButton, ToolbarActionView and ToolbarButton (or things that inherit from them). The menu items should be orthogonal.

I have re-bisected and found a different range:

You are probably looking for a change made after 597970 (known good), but no later than 598000 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/af2a58e78624def33f245d42d4b9eb902226848e..374107533c70d2e82337f3927b92218ab0d2126e

Note that there is a *different* brokenness in the menus, the submenu triangles are distorted. That is a *different* bug,  bug 894206 , and bisects to a different range.

To be clear, there should be a thin area of white _after_ the last menu item, but this bug is about how the bottom of the menu is exactly the same as the bottom of the last menu item which is wrong.

https://chromium.googlesource.com/chromium/src/+/db163611c6f71edee205d1a210464949f6f53f42 sounds like a more reasonable suspect then.

Yep, it's the commit mentioned in comment 5. Will revert.

Nicolas:

Your commit https://chromium-review.googlesource.com/c/chromium/src/+/1258045 broke menus. It does not revert cleanly. Please fix.

Thank you all for your quick help :)

 Issue 894338  has been merged into this issue.

FYI, it doesn't revert cleanly because https://chromium-review.googlesource.com/c/chromium/src/+/1271780 landed on top of it. If we revert that we should be able to revert it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/1e0704e6fc64ffadb72ba89035447ba1fc690426

commit 1e0704e6fc64ffadb72ba89035447ba1fc690426
Author: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Date: Tue Oct 16 06:02:50 2018

Reland: Add footnote support to top-level menus

Adds a function to |MenuDelegate| that can be overloaded to create a
footnote View for a top-level menu.

The footnote view is rendered at the bottom of the menu, with a
different background color, similar to
|BubbleFrameView::SetFootnoteView()|.

Bug:  889229 ,  894193 
Change-Id: Icb67740fddfe03a7a2d9bae7c70b383cfe6a9845
Reviewed-on: https://chromium-review.googlesource.com/c/1277573
Reviewed-by: Michael Wasserman <msw@chromium.org>
Commit-Queue: Nicolas Ouellet-Payeur <nicolaso@chromium.org>
Cr-Commit-Position: refs/heads/master@{#599881}
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/BUILD.gn
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/bubble/bubble_frame_view.cc
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/bubble/bubble_frame_view.h
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/bubble/bubble_frame_view_unittest.cc
[add] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/bubble/footnote_container_view.cc
[add] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/bubble/footnote_container_view.h
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/controls/menu/menu_delegate.cc
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/controls/menu/menu_delegate.h
[add] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/controls/menu/menu_footnote_unittest.cc
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/controls/menu/menu_scroll_view_container.cc
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/controls/menu/menu_scroll_view_container.h
[modify] https://crrev.com/1e0704e6fc64ffadb72ba89035447ba1fc690426/ui/views/controls/menu/submenu_view.cc