The Runnable markers in the profilers are handy, but miss many types of
runnables. This includes most of those that wrap another runnable and run that
at a (possibly) later time.

AbstractThread, TaskDispatcher and TaskQueue does this for e.g. tail dispatched
tasks.

TaskQueueWrapper does this when wrapping webrtc tasks (and Mozilla Runnables) to
be run in a Mozilla TaskQueue with some overhead on the stack.

DelayedRunnable wraps a runnable to be run after a timeout.

It would perhaps be better in many cases to ignore the intermediate runnables,
but I haven't seen a straight forward way to achieve this.

More detailed data could be added on a case by case basis, for instance the
delay for a DelayedRunnable (incl. actual vs. target delay) or the scope of a
task in which a tail-dispatched runnable was dispatched. But this is also true
for the status quo (for instance the time from dispatch to run) so I leave these
ideas as future work.

Differential Revision: https://phabricator.services.mozilla.com/D135027