Okay, I found it. (It was hiding in a sub-dialog.)
Navigate to chrome://settings (or menu > “Settings”)
Under “Privacy” click the “Content settings…” button.
In the “Content settings” dialog:
b) select the “Do not allow…” choice, but add my.sketchup.com in the “Manage exceptions” sub-dialog.
You may need to do the same down in the ‘Pop-ups’ section as my.sketchup.com is likely to use some popup windows for the UI.