Revert of Revert of CrWinClang: Swarm content_unittests, net_unittests, unit_tests...

Revert of Revert of CrWinClang: Swarm content_unittests, net_unittests, unit_tests, browser_tests. (patchset #1 id:1 of https://codereview.chromium.org/869003004/)

Reason for revert:
Let's try this again now that the clang/win bots use fastbuild (crbug.com/455966)

Original issue's description:
> Revert of CrWinClang: Swarm content_unittests, net_unittests, unit_tests, browser_tests. (patchset #1 id:1 of https://codereview.chromium.org/859303007/)
>
> Reason for revert:
> Didn't work, isolate tests step still throws a MemoryError
>
> Original issue's description:
> > CrWinClang: Swarm content_unittests, net_unittests, unit_tests, browser_tests.
> >
> > Now that isolate archival no longer dies as quickly, this should work.
> >
> > BUG=446368, 419862
> > R=maruel@chromium.org
> >
> > Committed: https://chromium.googlesource.com/chromium/src/+/c1275273c2674e3b4a12e3e096dc5a6ae02374af
>
> TBR=maruel@chromium.org
> NOPRESUBMIT=true
> NOTREECHECKS=true
> NOTRY=true
> BUG=446368, 419862
>
> Committed: https://crrev.com/5dfdf4f834d542e7d5c81dc2f3fe34fb0265a9f3
> Cr-Commit-Position: refs/heads/master@{#312773}

TBR=maruel@chromium.org
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=446368, 419862

Review URL: https://codereview.chromium.org/893313006

Cr-Commit-Position: refs/heads/master@{#315508}