Currently when memory size references are updated with zero initial memory during GrowMemory/Relocation of Instance objects, the bounds check does not take into account the size of memtype.

R=titzer@chromium.org, bradnelson@chromium.org

Committed: https://crrev.com/70416a2b360c0d993cffb48284b143d484d1e290
Review-Url: https://codereview.chromium.org/2416543002
Cr-Original-Commit-Position: refs/heads/master@{#40326}
Cr-Commit-Position: refs/heads/master@{#40329}