Bug
1855376 - Free stacks of extra parallel markers between GCs r=sfink
We currently keep all mark stacks allocated after GC, shrunk to their default size.
For parallel marking we can free the mark stacks of all markers apart from the
first. If we fail to allocate them at the start of marking we can fall back to
not marking in parallel.
This fixes the AWSY regression.
The patch also changes GCMarker::reset() to cover everything that happens in
GCMarker::stop() so you don't need to call both.
Differential Revision: https://phabricator.services.mozilla.com/
D189342