Because this test uses heap verification, it is quite slow. Split it
into 4 smaller tests to avoid test timeout and allow them to be run
in parallel.

R=ahaas@chromium.org

Bug: 
Change-Id: Ie4ac841d1d8215019bb5cfcc335daea6b10ab789
Reviewed-on: https://chromium-review.googlesource.com/738146Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48998}