Backed out changeset 07a4682a75f2 (bug 956507) because it has bitrotten

Landed on a CLOSED TREE
Back out 2e7e2de7b13e (bug 948574) for b2g mochitest crashes
CLOSED TREE
Bug 932837 followup.  Don't use AutoJSContext in JSStackFrame, since we use that code on workers too.  r=bholley pending, but landing now to fix the CLOSED TREE.