If the interpreter has an upper limit of instructions to execute, treat
grow_memory like 1000 other instructions in order to account for the
huge execution time of grow_memory.

R=ahaas@chromium.org

Bug: chromium:807383
Change-Id: Id513a41257734a3041bef45bbc00c461fdec6787
Reviewed-on: https://chromium-review.googlesource.com/905605Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51149}