Checks async stack for late .then handlers with gc
foo1 (test.js:11:2)
-- Promise.then --
test (test.js:18:14)
(anonymous) (expr.js:0:0)

foo1 (test.js:11:2)
-- Promise.then --
test (test.js:22:14)
(anonymous) (expr.js:0:0)

foo1 (test.js:11:2)
-- Promise.then --
test (test.js:24:14)
(anonymous) (expr.js:0:0)