d8 was recently changed to keep running until wasm compilation has
completed. This adds a message test to test that.

R=ahaas@chromium.org

Change-Id: I73af53b6df4ee5f9a6afd26cf2d71a269140465f
Reviewed-on: https://chromium-review.googlesource.com/966184Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52008}