UMA: Add metrics for policy related OAuth token fetch for child user

Bug: 839025
Test: UserCloudPolicyTokenForwarderTest
Change-Id: I44c4973d09e52f75f57bd3fe35c693a083dcb649
Reviewed-on: https://chromium-review.googlesource.com/c/1399516
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Reviewed-by: Maksim Ivanov <emaxx@chromium.org>
Reviewed-by: Lutz Justen <ljusten@chromium.org>
Commit-Queue: Aga Wronska <agawronska@chromium.org>
Cr-Commit-Position: refs/heads/master@{#624166}
4 files changed