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This CL refactors InputScrollElasticityController and introduces 2 new
subclasses - InputScrollElasticityControllerBezier will be used for
managing Windows based overscroll and bounce back. The other subclass
InputScrollElasticityControllerExponential will be used on Mac for the
same purpose.

The CL also allows an overscrolled root scroller to "bounce back" via
an animation based on a Bezier curve. This animation is driven by
OverscrollBounceController::Animate. The duration of this animation is
determined by how far the scroller has been stretched. At every "tick"
of the animation, the progress of the animation is determined based on
the elapsed time. Animating flings will be added in a follow up CL.

Bug: 1058071
Change-Id: Ia4278105eac5cadae191a50c25654c88a92c5a33
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2231254
Commit-Queue: Rahul Arakeri <arakeri@microsoft.com>
Reviewed-by: Robert Flack <flackr@chromium.org>
Reviewed-by: David Bokan <bokan@chromium.org>
Reviewed-by: Philip Rogers <pdr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#791431}