DevTools: Initial implementation of line-level CPU profile.
The JS CPU profile is available when there's a recorded timeline with a JS profile.
It is put behind an experiment.
Things to do:
- support source maps.
- make it possible to hide profile without reseting timeline.
BUG=
590936
Committed:
https://crrev.com/18c02c057c1d9d9938341fb2f4dcad2a3aef9acc
Cr-Commit-Position: refs/heads/master@{#380873}