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This CL is to record input delay UKM which is defined as the duration
between the hardware timestamp and the start of event processing on the
main thread for the meaningful input.

UKM Privacy Review:
https://docs.google.com/document/d/1VQvmb3x7uGMmt2JvKt3_4zk1SPWHPB3yJSiyec7hY20

Bug: 1042004
Change-Id: I69eb91955f116e1f90b9b72a7d3dd13b449fa4ff
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2008436Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Bryan McQuade <bmcquade@chromium.org>
Reviewed-by: Nate Chapin <japhet@chromium.org>
Commit-Queue: Hongbo Song <hbsong@google.com>
Cr-Commit-Position: refs/heads/master@{#736527}