Profile extension host when needed

[jrieken]

We finally have all pieces to automatically start profiling the extension host when it goes dark. This is a flow I would like to have:

• detect that the extension host is unresponsive (by waiting for the ack-messages)
• attach the profiler and profile for a bit
• associate time slices from the profile to extensions (just like the Running Extension View does it after profiling)
• show a message to file a bug against the heaviest hitters...

[jrieken]

cc @egamma

[jrieken]

With today's insiders build we start profiling the extension host as soon as it is found to be unresponsive. Finding are currently send as telemetry and logged down as message: