This CL fixes the copy-within JSTest benchmark so it works on Android.

R=machenbach@chromium.org

Change-Id: I63662f9ab00d0199614681a53118bc4079e697ff
Reviewed-on: https://chromium-review.googlesource.com/1168488Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Simon Zünd <szuend@google.com>
Cr-Commit-Position: refs/heads/master@{#55001}