Add metrics for allowlist lookup

To determine if we need to make local allowlist lookup async,
we'd like to record the time for a lookup.

Bug: 999344
Change-Id: If029d9bc678aaeeb17ca388337d0f1ec2f51dddf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1797333
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Reviewed-by: Varun Khaneja <vakh@chromium.org>
Commit-Queue: Xinghui Lu <xinghuilu@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695894}
2 files changed