Reland "Unify input delay computations for UMA, UKM, and EventTiming"

This is a reland of ae50f0f08fad0ff02cffc9923fed3d4ed6e6d62f

Original change's description:
> Unify input delay computations for UMA, UKM, and EventTiming
>
> This CL moves the input delay computations for UKM to further down the
> pipeline to where they are computed for EventTiming. After this CL, the
> same types of events are logged by both UMA/UKM and EventTiming. The
> WebViewTest is fixed so that the artificial events move further enough
> down the pipeline. The tests checking for pointerCancels are no longer
> applicable since these only applied to the UMA/UKM computations, per
> issue 924278.
>
> By unifying input delay computation, this CL also fixes frame
> attribution for the UMA/UKM input delays: PageWidgetDelegate does not
> know the target frame (before, it would tell the root that an event has
> occurred even if it occurred in an iframe.
>
> Bug: 897656, 925130
> Change-Id: I27dba1cbb82ad780d21166a5469001e266612a78
> Reviewed-on: https://chromium-review.googlesource.com/c/1476070
> Reviewed-by: Steven Holte <holte@chromium.org>
> Reviewed-by: Charlie Harrison <csharrison@chromium.org>
> Reviewed-by: Dave Tapuska <dtapuska@chromium.org>
> Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#635687}

TBR=dtapuska@chromium.org, holte@chromium.org

Bug: 897656, 925130
Change-Id: Ifa253657428ee7a04d3af7b06257482d7e948b58
Reviewed-on: https://chromium-review.googlesource.com/c/1496336
Reviewed-by: Nicolás Peña Moreno <npm@chromium.org>
Reviewed-by: Charlie Harrison <csharrison@chromium.org>
Commit-Queue: Nicolás Peña Moreno <npm@chromium.org>
Cr-Commit-Position: refs/heads/master@{#636827}
18 files changed