Similar to wasm, do also mask memory accesses from asm.js code as an
additional protection against OOB accesses.

R=ahaas@chromium.org
CC=titzer@chromium.org, mstarzinger@chromium.org

Change-Id: Iee7124c6d6078fb52cd1caa37b013c919c5505fb
Reviewed-on: https://chromium-review.googlesource.com/833914Reviewed-by: Andreas Haas <ahaas@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50205}