'ref' builds might not yet have BigInt support. Instead of crashing
when the benchmark file is loaded, the benchmark now fails during
setup.

R=jgruber@chromium.org

Bug: chromium:834654
Change-Id: I2c03aeba4b6af947061504c369b5228d7b344307
Reviewed-on: https://chromium-review.googlesource.com/1019100
Commit-Queue: Simon Zünd <szuend@google.com>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52685}