Step 1. Click Open popups to register more Chrome CGWindowIDs in the browser-process ScopedCGWindowID map.
Step 2. Click getDisplayMedia() repeatedly. Each click
advances active_picker_source_id_ by 1. When the macOS
SCContentSharingPicker appears, pick any non-Chrome window
(e.g. Terminal, Finder). If the counter collides with a Chrome
CGWindowID on that attempt, the video below will show a Chrome
window you did not pick.
Tip: you can dismiss the OS picker (Esc) on most attempts to keep
advancing the counter cheaply — the increment happens on
Open(), before any selection.