Bug 1243001 part 4. Switch to using MaybeResolve/MaybeReject instead of ResolveInternal/RejectInternal for PromiseWorkerProxy. r=peterv

This is the one part of this set of patches that is actually a substantive change
even without SPIDERMONKEY_PROMISE defined.  This is being done because I don't
want to create ResolveInternal/RejectInternal methods on dom::Promise in the
new world.

In practice, the difference between MaybeResolve/Reject and
ResolveInternal/RejectInternal is that the former will do nothing if the
Promise is "resolved" in terms of spec terminology: either settled or locked in
to track another Promise.  A resolved but still pending Promise can still get
fulfilled (what we call ResolveInternal) or rejected when the promise it's
tracking settles.

So the difference only matters if PromiseWorkerProxy can be working with a
"resolved" Promise (in which case what it's doing now would settle it, while
what I'm switching to would not).  But I don't believe PromiseWorkerProxy ever
points to a "resolved" Promise.

dom/promise/Promise.cpp

@@ -2547,14 +2547,14 @@ void
 PromiseWorkerProxy::ResolvedCallback(JSContext* aCx,
                                      JS::Handle<JS::Value> aValue)
 {
-  RunCallback(aCx, aValue, &Promise::ResolveInternal);
+  RunCallback(aCx, aValue, &Promise::MaybeResolve);
 }
 
 void
 PromiseWorkerProxy::RejectedCallback(JSContext* aCx,
                                      JS::Handle<JS::Value> aValue)
 {
-  RunCallback(aCx, aValue, &Promise::RejectInternal);
+  RunCallback(aCx, aValue, &Promise::MaybeReject);
 }
 
 bool