Revert of Revert of Revert of Promise assimilation fix. (patchset #1 id:1 of https://codereview.chromium.org/1181533006/)

Reason for revert:
[Sheriff] Changes/breaks layout tests. Please land upstream needsmanualrebaseline requests first or fix the tests.

E.g.
http://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Win/builds/400
One test fails, one times out. See e.g. expectations changes:
https://storage.googleapis.com/chromium-layout-test-archives/V8-Blink_Win/400/layout-test-results/inspector/sources/debugger-async/async-callstack-promises-diff.txt

On linux debug theses tests crash:
http://build.chromium.org/p/client.v8.fyi/builders/V8-Blink%20Linux%2064%20%28dbg%29/builds/346
https://storage.googleapis.com/chromium-layout-test-archives/V8-Blink_Linux_64__dbg_/346/layout-test-results/results.html

Original issue's description:
> Revert of Revert of Promise assimilation fix. (patchset #1 id:1 of https://codereview.chromium.org/1176163004/)
>
> Reason for revert:
> Test failures are bogus. Snapshot blob and natives blob are out of sync due to build being weird.
>
> Original issue's description:
> > Revert of Promise assimilation fix. (patchset #8 id:160001 of https://codereview.chromium.org/1098663002/)
> >
> > Reason for revert:
> > Test failures: https://chromegw.corp.google.com/i/client.v8/builders/V8%20Linux64/builds/3829
> >
> > Original issue's description:
> > > Promise assimilation fix.
> > >
> > > Let x be a fulfilled promise and y be another promise. |x.then(() => y)|
> > > should call |y.then|, but the current implementation calls PromiseChain.
> > > We can see the difference when we set a custom function to |y.then|.
> > >
> > > This CL fixes the spec violation, but as a result |then| is no longer
> > > a wrapper of |chain| and in some cases it does not work well with
> > > |accept| or |chain|. That is not a problem for ES6 promise users because
> > > ES6 promise doesn't have them.
> > >
> > > LOG=N
> > > BUG=477921
> > >
> > > Committed: https://crrev.com/2f57dff3ea0c45e1a61b334fda962460f89d71bc
> > > Cr-Commit-Position: refs/heads/master@{#28926}
> >
> > TBR=arv@chromium.org,caitpotter88@gmail.com,rossberg@chromium.org,yhirano@chromium.org
> > NOPRESUBMIT=true
> > NOTREECHECKS=true
> > NOTRY=true
> > BUG=477921
> >
> > Committed: https://crrev.com/5bb75f514027f79303396dba823c2d78c6add83b
> > Cr-Commit-Position: refs/heads/master@{#28927}
>
> TBR=arv@chromium.org,caitpotter88@gmail.com,rossberg@chromium.org,yhirano@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=477921
>
> Committed: https://crrev.com/6f214bdd8bcdc76d48bd85c3bd897f0e2427ff95
> Cr-Commit-Position: refs/heads/master@{#28928}

TBR=arv@chromium.org,caitpotter88@gmail.com,rossberg@chromium.org,yhirano@chromium.org,yangguo@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=477921

Review URL: https://codereview.chromium.org/1181603003

Cr-Commit-Position: refs/heads/master@{#28931}