This flow has been removed from Chromium.

Chromium changes:

https://bugs.chromium.org/p/chromium/issues/detail?id=956680

https://chromium.googlesource.com/chromium/src/+/afd6d11e54a3682cf1e4d0476e598eb234488246

commit afd6d11e54a3682cf1e4d0476e598eb234488246
Author: Hector Carmona <hcarmona@chromium.org>
Date:   Mon Jun 24 21:07:42 2019 +0000

    Navi: Delete entry point for showing chrome://welcome-win10

    Bug: 956680

https://chromium.googlesource.com/chromium/src/+/9359944557ddce6a63516df681eb38e0a70829df

commit 9359944557ddce6a63516df681eb38e0a70829df
Author: Hector Carmona <hcarmona@chromium.org>
Date:   Wed Jun 26 17:56:25 2019 +0000

    Navi: Deprecate kHasSeenWin10PromoPage pref.

    Bug: 956680