[DNT] Fix recording of backfalsing

The current implementation does not verify if the first navigation
is triggered by a back/forward gesture or a back/forward button. The
histogram will be recorded even if the first navivation is triggered
by clicking on a link.

This Cl ensures the histgoram is recorded only when the first
navigation is triggered by a navigation gesture or a navigation button.

OBSOLETE_HISTOGRAM[Android.BackPress.Backfalsing] = replaced by
Android.BackPress.Backfalsing2

Bug: 378728705
Change-Id: I4507e82b2a3f4c24f696791b26696e4550426224
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6363083
Reviewed-by: Theresa Sullivan <twellington@chromium.org>
Commit-Queue: Lijin Shen <lazzzis@google.com>
Reviewed-by: Wenyu Fu <wenyufu@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1435181}