Resolve OOMing with multiple tabs open

[Paul Irish]

Yeah if you open a dozen trace cafes you get lots of trace cafe renderers but one huge devtools frontend process
With a main thread that drowns

The iframe attributes credentialless referrerpolicy nor sandbox seem to affect the process sharing behavior. will need to see if there's another mechanism we can use to get them split into separate processes.

That and/or fix the large memory consumption. :)