Reland "chrome: run tools/media_engagement_preload/make_dafsa.py in python3"

This reverts commit e30fcda2ebf55ecb2a6a4c3cbeb62028611fbdf9.

Reason for revert:
use python3 instead of vpython3 explicitly in
chrome/browser/media/media_engagement_autoplay_browsertest.cc


.vpython3 change is for PRESUBMIT.py which uses vpython3 by default.

Original change's description:
> Revert "chrome: run tools/media_engagement_preload/make_dafsa.py in python3"
>
> This reverts commit 07e05386c5d83fb0d428b3a847ee4ddac4b20bfd.
>
> Reason for revert: MediaEngagementAutoplayBrowserTest is failing on mac bots:
> https://ci.chromium.org/ui/p/chromium/builders/ci/Mac10.11%20Tests/63046/overview
> https://ci.chromium.org/ui/p/chromium/builders/ci/Mac10.12%20Tests/43848/overview
>
> Original change's description:
> > chrome: run tools/media_engagement_preload/make_dafsa.py in python3
> >
> > Fixed: 1210295
> > Change-Id: I531f99ba4209086c25157854321e3addf1ce632e
> > Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2903407
> > Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
> > Reviewed-by: Dirk Pranke <dpranke@google.com>
> > Reviewed-by: Sergey Ulanov <sergeyu@chromium.org>
> > Commit-Queue: Sergey Ulanov <sergeyu@chromium.org>
> > Cr-Commit-Position: refs/heads/master@{#884796}
>
> Change-Id: I4bb812fa3ddbfba0450574edf1e4b8e8d36c01eb
> No-Presubmit: true
> No-Tree-Checks: true
> No-Try: true
> Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2909213
> Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
> Commit-Queue: Tim Sergeant <tsergeant@chromium.org>
> Owners-Override: Tim Sergeant <tsergeant@chromium.org>
> Reviewed-by: Takuto Ikuta <tikuta@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#884891}

Change-Id: I5246afcacdf289da798240c60fafd530b8ef60ae
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2908796
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Reviewed-by: Nico Weber <thakis@chromium.org>
Reviewed-by: Dirk Pranke <dpranke@google.com>
Commit-Queue: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#885449}