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This change will suppress all fling cancel events unless the last event
was a fling event. Also it generates a proper sequence of a scroll
event with zero distance.

BUG=590754
TEST=Fling and touch the touchpad after fling. Should stop scrolling
motion in android apps.

Review-Url: https://codereview.chromium.org/2840113002
Cr-Commit-Position: refs/heads/master@{#469403}