Use ui events to latch while scrolling by touchpad on chrome book.

Scrolling with trackpad on Chrome devices generates GFC when the user
touches the touchpad and GFS when the user lifts their fingers even when
fling velocity is zero. This cl uses these events for scroll latching
instead of the timer. Scrolling with a real mouse wheel is unchanged.

       TouchpadFlingStartResetsWheelPhaseState

Bug: 526463
Test: RenderWidgetHostViewAuraWheelScrollLatchingEnabledTest.
Change-Id: Ie3bb30c57fc8fd50f543d2856e570e401f5a2caf
Reviewed-on: https://chromium-review.googlesource.com/757577
Commit-Queue: Sahel Sharifymoghaddam <sahel@chromium.org>
Reviewed-by: Timothy Dresser <tdresser@chromium.org>
Cr-Commit-Position: refs/heads/master@{#516351}
4 files changed