Add `console.probe()` API and inspector instrumentation to plumb
samples towards the inspector infrastructure.
Add probe agent for inspector, dummy DataProbe interface, and
stubbed-out Probe inspector protocol domain.
Reimplement DOMTimer capture and replay.

The old implementation bitrotted with upstream changes to how timer ids
were acquired. The code was getting hairy, so it's been re-implemented
with `DOMTimer` subclasses. Timer id acquisition and initial scheduling
has been moved out of the constructor.

Closes #263.
Flesh out the implementation of ScriptProbeServer so that it looks up
and samples applicable probes during execution.

Add machinery to ProbeAgent so it can resolve and modify probes as
scripts are loaded or destroyed.
Remove code that attempts to disable the WebProcess sandbox when
ENABLE(TIMELAPSE), since it doesn't actually do so. This was somehow
causing file:/// resources to fail to load.