I'm suspecting this change.

The item with id="add_comment_panel" and class="addCommentsContainer" is left positioned and is on top of the drop panel that is drawn causing the graphics glitch. It appears centered in FireFox. So I'm not sure this is intended or not but it sounds like a default has change so perhaps it is.


commit	b80c579439ab737f82cddb5c73c91bc1daacd354	
author	cbiesinger <cbiesinger@chromium.org>	Wed Apr 27 19:53:33 2016
committer	Commit bot <commit-bot@chromium.org>	Wed Apr 27 19:54:36 2016
[css-flexbox] Implement new abspos handling

The spec no longer requires us to position abspos items as if they
were 0x0 flex items. Instead, they should be positioned as if they were
the sole flex item in the flexbox, i.e. they should respect the align-items
and justify-content properties:
https://drafts.csswg.org/css-flexbox/#abspos-items

Intent to implement and ship:
https://groups.google.com/a/chromium.org/d/topic/blink-dev/MMdPt_5omT4/discussion

BUG= 517265 

Review-Url: https://codereview.chromium.org/1920453003
Cr-Commit-Position: refs/heads/master@{#390154}

This was an intentional change to match the latest specification.

Indeed. Note that Edge positions the element the same way, though oddly it doesn't paint it over the files popup.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/462304822ad58b7755e9de924c8cda4af093160e

commit 462304822ad58b7755e9de924c8cda4af093160e
Author: tsergeant <tsergeant@chromium.org>
Date: Thu Sep 22 01:00:19 2016

History: Fix flicker of sync notices when loading new data

The history page shows a notice when showing synced results from other
devices. This notice would frequently flicker when loading in new
results (eg, from a search), which was particularly noticable on the MD
History page, where this can cause toolbar elements to move around.

This fixes the issue by only resetting notice status back to false
when there is no web history service. In all other cases, we can
rely on the call to web history to reset the sync notices to their
correct values.

BUG= 628555 

Review-Url: https://codereview.chromium.org/2354053003
Cr-Commit-Position: refs/heads/master@{#420220}

[modify] https://crrev.com/462304822ad58b7755e9de924c8cda4af093160e/chrome/browser/ui/webui/browsing_history_handler.cc