This is a reland of fffa4555.

The win asan bots use win10 now which should fix the problems.

Original change's description:
> [build] Prepare switching win asan to 64 bits
>
> This switches the current win32 bots to win32 under the hood in MB. We'll
> remove them and replace them with win64 bots in a follow up on the infra
> side.
>
> This also infers the clang option from asan, because on windows we need
> to set clang explicitly.
>
> TBR=sergiyb@chromium.org
>
> Bug: chromium:786303
> Change-Id: I9dddd5050a21a364c302a761ff15ddd21e97c7dc
> Reviewed-on: https://chromium-review.googlesource.com/883103
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#50828}

TBR=sergiyb@chromium.org

Bug: chromium:786303
Change-Id: Ie344a7b6b16f575a061d13b5c3792fc9bd862734
Reviewed-on: https://chromium-review.googlesource.com/883522Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#50850}