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 The tests checking for pointerCancels are no longer
applicable since these only applied to the UMA/UKM computations, per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}
18 files changed