Also contains folded version of the following patches that have to land at the same time with enabling the new implementation (or be backed out at the same time, if it comes to that):
Add Promise checks to test_xrayToJS.xul. r=bholley
Change Promise debugger hook tests to use Promise ctor instead of makeFakePromise. r=shu
Change DOM interface tests to assume Promise is an ES builtin, not a DOM one. r=bz
Remove some PromiseDebugging references. r=bz
Adapt promise rejections test to new xray-unwrapping error. r=bz
Fix expectations in browser_timelineMarkers tests. r=tromey
f8bc4fae19