Collect UMA data for SiteIsolatedCodeCache

Adds SiteIsolatedCodeCache.Behavour histogram. This collects the
behaviour of site isolated code cache for each request received.
It records if the request was serviced and if serviced how it was
serviced for ex: hit, miss, update.

Bug: chromium:812168
Change-Id: Ie9e45af8e72dee6fafc1b088c139b7b87fcc0851
Reviewed-on: https://chromium-review.googlesource.com/1196430
Reviewed-by: Brian White <bcwhite@chromium.org>
Reviewed-by: Kinuko Yasuda <kinuko@chromium.org>
Commit-Queue: Mythri Alle <mythria@chromium.org>
Cr-Commit-Position: refs/heads/master@{#588047}
4 files changed