A few tests that would be good to have to verify that the known manifestations
of this bug are resolved.

Previously, the async generator and async function tests would crash. The other
ones never did, but still resulted in the register overwite bug.

BUG=v8:6322
R=adamk@chromium.org

Change-Id: Ic2238227629077de5671d67d18b3bfe018dd23f4
Reviewed-on: https://chromium-review.googlesource.com/514230Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Cr-Commit-Position: refs/heads/master@{#45524}