A change which sped up hot restart locally caused many of the devicelab measures to regress. I think this is because we do not measure when the isolate is actually "ready", so starting a reload or restart prematurely can cause time spent doing initialization to be registered as part of the reload operation.

A fix for this would be to have the framework include some sort of "initialization complete" event ... but it is not clear what the correct trigger would be. Perhaps after the first frame is successfully registered?

(9a3a0dc1 caused the benchmark regression - possibly since we spend less time syncing files now so we start the restart earlier)