This reverts commit ee3729d2.

Reason for revert: The initial commit required https://chromium-review.googlesource.com/c/510021/ also land on the Blink side. I mistakenly thought it did.

Original change's description:
> Revert "[wasm] Remove override-ability from async compile and instantiate."
> 
> This reverts commit 2869dd55.
> 
> Reason for revert: Breaks:
> https://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064/builds/15850
> 
> See also:
> https://github.com/v8/v8/wiki/Blink-layout-tests
> 
> Original change's description:
> > [wasm] Remove override-ability from async compile and instantiate.
> > 
> > We're now using explicit APIs.
> > 
> > Bug: 
> > Change-Id: I4a4248e44543f6e7dfcbdc66456e610fb98ff5ee
> > Reviewed-on: https://chromium-review.googlesource.com/513406
> > Commit-Queue: Brad Nelson <bradnelson@chromium.org>
> > Reviewed-by: Brad Nelson <bradnelson@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#45500}
> 
> TBR=bradnelson@chromium.org,mtrofin@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> 
> Bug: 
> Change-Id: Ie7c2db40279bd07c535c20afaa1cea51b680fe65
> Reviewed-on: https://chromium-review.googlesource.com/513862
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#45502}

TBR=bradnelson@chromium.org,machenbach@chromium.org,mtrofin@chromium.org,v8-reviews@googlegroups.com
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true

Bug: 
Change-Id: Ib826b590b5d362d005460fcebdc6800c8d6c5f63
Reviewed-on: https://chromium-review.googlesource.com/513496Reviewed-by: Mircea Trofin <mtrofin@chromium.org>
Commit-Queue: Mircea Trofin <mtrofin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45519}