This is tied to ui::LatencyInfo which needs a rework for Viz

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/79a0b472acdfcdfdb4f9a223af85c2f3529612c4

commit 79a0b472acdfcdfdb4f9a223af85c2f3529612c4
Author: Sadrul Habib Chowdhury <sadrul@chromium.org>
Date: Mon Mar 12 22:10:57 2018

viz: Fix a content_browsertests.

ScrollLatencyBrowserTest.SmoothWheelScroll waits for an UMA metric to
be collected. With OOP-D, the metric is collected in the gpu process,
instead of in the browser process. So, make sure the test collects
all the UMA from the child processes so that it can see the UMA it is
waiting for.

BUG= 786151 

Change-Id: I58d93c32c4ee57b1f8ba24de1a370bac97f0e17f
Reviewed-on: https://chromium-review.googlesource.com/959454
Commit-Queue: Sadrul Chowdhury <sadrul@chromium.org>
Reviewed-by: Jonathan Ross <jonross@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542622}
[modify] https://crrev.com/79a0b472acdfcdfdb4f9a223af85c2f3529612c4/content/browser/renderer_host/input/scroll_latency_browsertest.cc
[modify] https://crrev.com/79a0b472acdfcdfdb4f9a223af85c2f3529612c4/testing/buildbot/filters/viz.content_browsertests.filter

This should now be fixed and turned on.