Manual regression range:
Good Build: 56.0.2900.0 
Bad Build:  56.0.2901.4 

Deleted: Actual_List.mp4 429 KB

	Actual_List.mp4 429 KB View Download

Deleted: Expected_List.mp4 438 KB

	Expected_List.mp4 438 KB View Download

Using the per-revision bisect providing the bisect results,
Good build: 56.0.2900.0 (Revision: 427219).
Bad build: 56.0.2901.4 (Revision: 427541).

You are probably looking for a change made after 427247 (known good), but no later than 427248 (first known bad).
CHANGELOG URL:
  https://chromium.googlesource.com/chromium/src/+log/51e832338dfaeedf418778541a10003fd1feef8b..9811dce8931bffbbdc9ae70e8e362491c3de4157

@dpapad -- Could you please look into the issue, pardon me if it has nothing to do with your changes and if possible please assign it to concern owner.
Thank You.

I am able to reproduce this, only when going up to 200%. Also closing the wrongly positioned menu and re-opening it makes it show in the correct location. Guessing it could be a blink bug, but not sure yet. Either way I think it is a P3.

I confirmed that this is a Blink bug. getBoundingClientRect() is returning wrong values (specifically for 'left') when the zoom level gets to 200% (see screencast for repro).

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	get_client_rect.mp4 739 KB View Download

Un-assigning myself so that someone from the Blink team can pick this up.

Just to update:

Still able to reproduce the issue on mac 10.11.6 chrome version 57.0.2931.0

Could someone from blink team take a look please

FYI: Please do *not* assign bugs when switching components, that sidesteps the triage process and greatly increases the delay before anyone sees the bug.

When zooming in when the menu is open the menu element is not repositioned but instead hidden but remains in the DOM, it is then re-shown before being repositioned when clicking the three-dot-icon again trigger overflow and in turn scrolling which affects the metrics return by getBoundingClientRect.

This is a bug in the application, not in Chrome.
Always position *before* showing elements to avoid overflow, focus issues and problems like this.

> Always position *before* showing elements to avoid overflow

Can you elaborate a bit on this? The logic in question is at https://cs.chromium.org/chromium/src/ui/webui/resources/cr_elements/cr_action_menu/cr_action_menu.js?q=cr_action_menu.js&sq=package:chromium&dr&l=133,137, where I have to call showModal() on the dialog first, so that I can then use offsetWidth and offsetHeight to position it exactly where it needs to be (otherwise offsetWidth/offsetheight are not populated yet).