Test that unicode identifiers can be used for imports and exports, and
that unicode function names appear correctly in error messages.

R=ahaas@chromium.org

Change-Id: Ic6ac77159c275845886b2eb779cf59edb8cba9ea
Reviewed-on: https://chromium-review.googlesource.com/548315
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46220}