Sadrul says this is how we track mouse-wheel:

https://www.google.com/url?q=https://cs.chromium.org/chromium/src/ui/latency/latency_tracker.cc?type%3Dcs%26sq%3Dpackage:chromium%26l%3D213&sa=D&ust=1515263693234000&usg=AFQjCNE_3-HtnT5cfH8LLIx_vjCwAPH8VA

We should do something similar to track mouse-press and mouse-move. We'll also need to verify these make it to uma-histograms. Here's a histogram:

https://cs.chromium.org/chromium/src/ui/latency/latency_tracker.cc?type=cs&sq=package:chromium&l=262

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/849123e80609db2fa80f0cdfa5aa0a973a98af0c

commit 849123e80609db2fa80f0cdfa5aa0a973a98af0c
Author: Elliot Glaysher <erg@chromium.org>
Date: Thu Jan 11 22:40:34 2018

Add a metric for mouse events in LatencyTracker.

Bug:  798775 
Change-Id: I21dceea4719da385103eed485e0d99d945469c72
Reviewed-on: https://chromium-review.googlesource.com/852443
Reviewed-by: Tom Sepez <tsepez@chromium.org>
Reviewed-by: Robert Kaplow <rkaplow@chromium.org>
Reviewed-by: Sadrul Chowdhury <sadrul@chromium.org>
Commit-Queue: Elliot Glaysher <erg@chromium.org>
Cr-Commit-Position: refs/heads/master@{#528788}
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/content/browser/renderer_host/render_widget_host_impl.cc
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/tools/metrics/histograms/histograms.xml
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/ui/events/event.cc
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/ui/latency/latency_info.h
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/ui/latency/latency_tracker.cc
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/ui/latency/mojo/latency_info.mojom
[modify] https://crrev.com/849123e80609db2fa80f0cdfa5aa0a973a98af0c/ui/latency/mojo/latency_info_struct_traits.cc