These tests are also used for streaming. This CL changes the test to
actually output the exception that unexpectedly happened.

R=ahaas@chromium.org

Bug: v8:7921
Change-Id: Ia9c91a7d3d9452f9c0180329a5434f049b56c3c8
Reviewed-on: https://chromium-review.googlesource.com/c/1319755
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57284}