Chrome Version       : 69.0.3497.100
OS Version: OS X 10.13.6
URLs (if applicable) :
Other browsers tested:
  Add OK or FAIL after other browsers where you have tested this issue:
     Safari: OK

What steps will reproduce the problem?
1. Open ~100 Chrome tabs in ~25 windows.
2. Connect external Acer B326HK
3. In Displays preference pane, choose "Scaled" resolution and select some option not at either extreme.

What is the expected result?
Chrome should not run especially slowly.

What happens instead of that?
Chrome slows down tremendously. Switching tabs, clicking on UI elements (especially links), scrolling, closing tabs, etc all take multiple seconds, sometimes up to 30 seconds.


Please provide any additional information below. Attach a screenshot if
possible.

UserAgentString: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36

This happened with the Chrome 69 upgrade. Shutting down tabs seems to ameliorate the problem; running the external monitor at native resolution also fixes it. Note: I am also running with the built-in Retina display active; I have not tried to see if shutting that and running clamshell helps.