Isolated iframe process

Repro steps:
  1. Load this page ✔.
  2. Open Chrome's task manager, sort by CPU
  3. Observe 'Subframe: https://googleusercontent.com/' at the top, get the process ID
  4. Close the tab
  5. Observe process disappears from taskmanager
  6. Run 'top'- observe the process is still there, consuming 100% CPU