Repeatedly allocating >1GB fails on stress bots, hence run a GC
in-between to free the array buffer.

R=titzer@chromium.org
CC=​mlippautz@chromium.org, ulan@chromium.org

Bug: v8:6924
Change-Id: I44761e83f62b8225148eecbc569748cd3be21d6a
Reviewed-on: https://chromium-review.googlesource.com/718109Reviewed-by: Ben Titzer <titzer@chromium.org>
Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48541}