Renaming VR metrics class to indicate its scope

A small bit of cleanup work following on
https://chromium-review.googlesource.com/c/chromium/src/+/949052

Change-Id: I52da7165e2c8f7edc664cbd025cbbcbdaccd7252
Reviewed-on: https://chromium-review.googlesource.com/1000332
Commit-Queue: Anna Offenwanger <offenwanger@chromium.org>
Reviewed-by: Tibor Goldschwendt <tiborg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549662}
5 files changed