Tested the issue on Chrome Stable#53.0.2785.143, Canary 55.0.2879.0 on Mac OS X 10.12 and was able to reproduce the issue.

This is a Non-Regression issue seen from M30# 30.0.1549.0 (208818), marking the status to Untriaged so that the issue would get addressed.

Note: This is a Mac specific issue, not seen on Win and linux.
Thank You.

[mac triage] Reproduced this on Chrome 53.0.2785.143 OSX 10.11. Not reproducible on Safari.

The fade out animation of the select drop down on Mac is done by the OS, Chrome does not perform that animation.

Attached trace, we seem to simply stop rendering frames during the ~200ms fadeout.

Deleted: Screen Shot 2016-10-05 at 5.44.28 pm.png 153 KB

	Screen Shot 2016-10-05 at 5.44.28 pm.png 153 KB View Download

Deleted: trace_select-fadeout-mac.json.gz 2.1 MB

trace_select-fadeout-mac.json.gz 2.1 MB Download

 Issue 614810  has been merged into this issue.

+Victor can you help triage this bug to the right location?

It looks like we stop getting BeginFrames in the DisplayScheduler during this time.  enne@ are you familiar with this input on Mac?

No, I don't really know anything about it.  I'm happy to take a look after I finish looking at another regression, though.

I took a brief look and I think this is more mac-specific than I can fix.  As far as I can tell, it looks like this is related to the nested message loop in https://cs.chromium.org/chromium/src/content/browser/frame_host/popup_menu_helper_mac.mm?rcl=0&l=75.

Here's a quick trace where I clicked the select box, moused around for a little bit, and then chosen an option.  I did this a few times.  It looks like events are pumped while the select box is open and I mouse around, but as soon as I pick something (or cancel), then everything freezes across all processes for 300ms or so.  However, during both the mousing around and the freezing the nested message loop is running.  So, I'm not sure where the difference is.

Deleted: Screen Shot 2016-10-27 at 3.05.14 PM.png 240 KB

	Screen Shot 2016-10-27 at 3.05.14 PM.png 240 KB View Download

This is because the MessageLoop gets starved. When AppKit is closing the select menu, it is spinning a runloop in a mode that does not service the MessageLoop.

This CL https://codereview.chromium.org/2118883002/diff/1/base/message_loop/message_pump_mac.mm would fix it, but it may not be something we want to land.

 Issue 673284  has been merged into this issue.

r470769 is in Version 60.0.3097.0 canary and mostly resolves this. There is still a brief pause, but it's much shorter.

Nice work, this is almost perfect! Thank you.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/24ab401b3662d052facf19a169f553ea9a6bf7e1

commit 24ab401b3662d052facf19a169f553ea9a6bf7e1
Author: Trent Apted <tapted@chromium.org>
Date: Wed Sep 20 11:34:22 2017

Re-enable listening on private runloop modes, for a whitelist.

r470769 started observing private AppKit run loop modes to keep
UI and web pages responsive while menus were fading out, but it
interacted badly with app-modal dialogs.

This re-enables r470769, but only in 3 places:
 - Web page context menus
 - Web page <select> menus
 - menus run from toolkit-views UI.

      pause briefly when either the <select> menu or the right-
      click context menu are fading out. (The main menubar and the
      Chrome app/wrench menu still cause a brief pause when dismissed).

Bug:  726200 ,  602914 , 640466, 652007
Test: https://jsfiddle.net/kvmy8q9d/5/ - the animation shouldn't
Change-Id: Idf769c1f830ccb3ddc67205acb9e86aac2ec0460
Reviewed-on: https://chromium-review.googlesource.com/647836
Reviewed-by: Mark Mentovai <mark@chromium.org>
Reviewed-by: Avi Drissman <avi@chromium.org>
Commit-Queue: Trent Apted <tapted@chromium.org>
Cr-Commit-Position: refs/heads/master@{#503112}
[modify] https://crrev.com/24ab401b3662d052facf19a169f553ea9a6bf7e1/base/message_loop/message_pump_mac.h
[modify] https://crrev.com/24ab401b3662d052facf19a169f553ea9a6bf7e1/base/message_loop/message_pump_mac.mm
[modify] https://crrev.com/24ab401b3662d052facf19a169f553ea9a6bf7e1/base/message_loop/message_pump_mac_unittest.cc
[modify] https://crrev.com/24ab401b3662d052facf19a169f553ea9a6bf7e1/chrome/browser/ui/cocoa/renderer_context_menu/render_view_context_menu_mac.mm
[modify] https://crrev.com/24ab401b3662d052facf19a169f553ea9a6bf7e1/content/browser/renderer_host/webmenurunner_mac.mm
[modify] https://crrev.com/24ab401b3662d052facf19a169f553ea9a6bf7e1/ui/views/controls/menu/menu_runner_impl_cocoa.mm

 Issue 816446  has been merged into this issue.