Add a UMA histogram on forward progress made after path degrading

Change-Id: I795af410eadab4b68dae34f4c91dd59b312b264c
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4547281


Reviewed-by: Fan Yang <fayang@chromium.org>
Auto-Submit: Renjie Tang <renjietang@chromium.org>
Reviewed-by: David Schinazi <dschinazi@chromium.org>
Commit-Queue: Renjie Tang <renjietang@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1147432}