Don't create zero-velocity GestureFlingStarts.

ui/events/ozone/evdev/libgestures_glue/gesture_interpreter_libevdev_cros.cc

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/ozone/evdev/libgestures_glue/gesture_interpreter_libevdev_cros.h"
 
 #include <gestures/gestures.h>
 #include <libevdev/libevdev.h>
 #include <linux/input.h>
 
@@ skipping 315 matching lines @@
                   "Gesture Fling: (%f, %f) [%f, %f] fling_state=%d",
                   fling->vx,
                   fling->vy,
                   fling->ordinal_vx,
                   fling->ordinal_vy,
                   fling->fling_state);
 
   if (!cursor_)
     return;  // No cursor!
 
+  // We may receive a request for a GESTURE_FLING_START with zero velocity; in
+  // this case send a ET_SCROLL_FLING_CANCEL in case it's needed to stop a
+  // fling in progress.
+  // TODO(wjmaclean): is it possible to get consecutive GESTURE_FLING_STARTs?
+  bool should_fling_start = fling->fling_state == GESTURES_FLING_START &&
+                            (fling->vx != 0 || fling->vy != 0);
   EventType type =
-      (fling->fling_state == GESTURES_FLING_START ? ET_SCROLL_FLING_START
-                                                  : ET_SCROLL_FLING_CANCEL);
+      (should_fling_start ? ET_SCROLL_FLING_START : ET_SCROLL_FLING_CANCEL);
 
   // Fling is like 2-finger scrolling but with velocity instead of displacement.
   dispatcher_->DispatchScrollEvent(ScrollEventParams(
       id_, type, cursor_->GetLocation(), gfx::Vector2dF(fling->vx, fling->vy),
       gfx::Vector2dF(fling->ordinal_vx, fling->ordinal_vy),
       kGestureScrollFingerCount, StimeToTimeTicks(gesture->end_time)));
 }
 
 void GestureInterpreterLibevdevCros::OnGestureSwipe(const Gesture* gesture,
                                                     const GestureSwipe* swipe) {
@@ skipping 156 matching lines @@
 
 void GestureInterpreterLibevdevCros::ReleaseMouseButtons(stime_t timestamp) {
   DispatchMouseButton(BTN_LEFT, false /* down */, timestamp);
   DispatchMouseButton(BTN_MIDDLE, false /* down */, timestamp);
   DispatchMouseButton(BTN_RIGHT, false /* down */, timestamp);
   DispatchMouseButton(BTN_BACK, false /* down */, timestamp);
   DispatchMouseButton(BTN_FORWARD, false /* down */, timestamp);
 }
 
 }  // namespace ui