Bring the minimizeMemory() implementation up to date

[nmaier]

The toolkit (aboutMemory.js) implementation looks like this, these days:

function doMMU()
{
  Services.obs.notifyObservers(null, "child-mmu-request", null);
  gMgr.minimizeMemoryUsage(
  () => updateMainAndFooter("Memory minimization completed", HIDE_FOOTER));
}

While .minimizeMemoryUsage() is just the "3x memory-pressure notifications" dance in C++ at the moment, i.e. equivalent to what memchaser uses anyway, the child-mmu-request is the more interesting bit. Sending this notification will cause child processes to call .minimizeMemoryUsage(). And since there are child processes even on Desktop these days, e.g. the thumbnailer for about:home and "New e10s window" in Nightly, it would be good for memchaser to send the notification as well.

[whimboo]

Thanks Nils. We will try to get this into the 0.6 release.

[whimboo]

PR #196 has been fixed. Thanks!