This patch adds a test for async/await analogous to a previous Promise test.
It also fixes a typo in promise.js and makes a previous Promise test more
correct by ensuring that all assertions run before completion, fixing the
test expectations for the real result (which seems correct).

BUG=v8:4483
CQ_INCLUDE_TRYBOTS=tryserver.chromium.linux:linux_chromium_rel_ng;tryserver.blink:linux_blink_rel

Review-Url: https://codereview.chromium.org/2037653002
Cr-Commit-Position: refs/heads/master@{#36903}