The grow_memory opcode basically just executes a runtime call, but
needs to check a condition first, and convert to and from Smi.

R=titzer@chromium.org

Bug: v8:6600
Change-Id: If7d62a8bb0ca6d02bd47ef6048cc65da502b002b
Reviewed-on: https://chromium-review.googlesource.com/1042185
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Ben Titzer <titzer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52978}