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This change applies three heuristics to make trackpad scrolling feel
smoother. We increase the frequency at which we submit scroll events to
the platform, we also decrease the scroll scale factor (to make the
scrolls less jumpy), and we do some simple filtering of our scroll
values.

I pair-programmed much of this change with asimjour@ and he wrote the
initial code to interpolate events in the android ui gesture target.

Bug: 859075
Cq-Include-Trybots: luci.chromium.try:android_optional_gpu_tests_rel;luci.chromium.try:linux_optional_gpu_tests_rel;luci.chromium.try:linux_vr;luci.chromium.try:mac_optional_gpu_tests_rel;luci.chromium.try:win_optional_gpu_tests_rel
Change-Id: I2fe42940214d01d99618ddacd182f202ff271dad
Reviewed-on: https://chromium-review.googlesource.com/1120425Reviewed-by: Michael Thiessen <mthiesse@chromium.org>
Commit-Queue: Ian Vollick <vollick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#571535}