PolicyBlocklist metrics GWS variant and fine grained LCP

This patch adds some more PolicyBlocklist metrics variant
those will be recorded only for GWS to analyze why performance
impact is different on the target page.

This change also tries experimental LCP metric that is
recorded within a small range to capture small improvements.

Change-Id: I774dd1a8ebe47c733859599b08a073f4bf134094
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6054938
Reviewed-by: Minoru Chikamune <chikamune@chromium.org>
Commit-Queue: Takashi Toyoshima <toyoshim@chromium.org>
Code-Coverage: findit-for-me@appspot.gserviceaccount.com <findit-for-me@appspot.gserviceaccount.com>
Reviewed-by: Owen Min <zmin@chromium.org>
Auto-Submit: Takashi Toyoshima <toyoshim@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1391458}