GitLab

Add UMA logging of time taken to complete ML service requests,
as well as the time spent before a pending request is cancelled.
Also update the existing Smart Dim unit tests to verify that the logging
works.

Bug: 893425, 914640
Test: - Builds and boots, inference calls checked via logs on nocturne
      - All related unit tests still pass.

Change-Id: I542af752a0133939c65eaa435ed3f5be907140db
Reviewed-on: https://chromium-review.googlesource.com/c/1393670Reviewed-by: Jia Meng <jiameng@chromium.org>
Commit-Queue: Prashant Malani <pmalani@chromium.org>
Cr-Commit-Position: refs/heads/master@{#619892}