Revert of Temporarily revert just Multiply to see if that's the source of NEON diffs...

Revert of Temporarily revert just Multiply to see if that's the source of NEON diffs. (patchset #1 id:1 of https://codereview.chromium.org/1129293005/)

Reason for revert:
Diff's still there.  Multiply is not the culprit.

Original issue's description:
> Temporarily revert just Multiply to see if that's the source of NEON diffs.
>
> Local testing is confusing and inconclusive.  Pulling out the big guns.
>
> BUG=skia:
>
> Committed: https://skia.googlesource.com/skia/+/5b9f352ff1e245dd48e200f8f8b683f4569547d3

TBR=mtklein@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=skia:

Review URL: https://codereview.chromium.org/1143553004