Revert of Remove SIMD.js from V8. (patchset #7 id:120001 of https://codereview.chromium.org/2684313003/ )

Reason for revert:
red

Original issue's description:
> Remove SIMD.js from V8.
>
> LOG=Y
> BUG=v8:4124,5948
> R=bradnelson@chromium.org,bmeurer@chromium.org,jochen@chromium.org,hpayer@chromium.org,danno@chromium.org
> (notry since trybots can't patch directory deletes)
> NOTRY=true
>
> Review-Url: https://codereview.chromium.org/2684313003
> Cr-Commit-Position: refs/heads/master@{#43162}
> Committed: https://chromium.googlesource.com/v8/v8/+/d170c57ab996d00c4665a9d865bd5754a1806c6c

TBR=bmeurer@chromium.org,jochen@chromium.org,hpayer@chromium.org,danno@chromium.org,bradnelson@google.com,bbudge@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=v8:4124,5948

Review-Url: https://codereview.chromium.org/2692933002
Cr-Commit-Position: refs/heads/master@{#43164}