Ensure fling stops are sent before new gestures

In Chrome, fling stops are used as a signal that fingers have landed on
the touchpad. However, the gesture library would sometimes send a fling
stop after another gesture had started, or not at all in the case of
repeated scroll gestures.

This CL ensures that a fling stop is sent before every new gesture, and
when a finger lands without gesturing.

BUG=chromium:824565
TEST=manual testing ensuring flings are produced before every new
gesture, checking for regressions in touchtests

Change-Id: I6d748681a97db13ea835dac3936f9c85b3351f69
Reviewed-on: https://chromium-review.googlesource.com/1464563
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Sean O'Brien <seobrien@chromium.org>
Reviewed-by: Andrew de los Reyes <adlr@chromium.org>
4 files changed