Touchpad scroll latching enabled for Mac behind flag.

ui/events/blink/input_handler_proxy.cc

 // Copyright 2013 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/blink/input_handler_proxy.h"
 
 #include <stddef.h>
 
 #include <algorithm>
 
@@ skipping 113 matching lines @@
   return scroll_begin_event;
 }
 
 cc::ScrollState CreateScrollStateForGesture(const WebGestureEvent& event) {
   cc::ScrollStateData scroll_state_data;
   switch (event.type) {
     case WebInputEvent::GestureScrollBegin:
       scroll_state_data.position_x = event.x;
       scroll_state_data.position_y = event.y;
       scroll_state_data.is_beginning = true;
+      // On Mac flings are aslo scrolls.

[tdresser, 2016/08/18 13:59:47]

aslo -> also

Or perhaps:
// On Mac, a GestureScrollBegin in the inertial phase indicates a fling start.

[sahel, 2016/08/18 15:41:56]

Done.

+      if (event.data.scrollBegin.inertialPhase ==
+          WebGestureEvent::MomentumPhase)
+        scroll_state_data.is_in_inertial_phase = true;
       break;
     case WebInputEvent::GestureFlingStart:
       scroll_state_data.velocity_x = event.data.flingStart.velocityX;
       scroll_state_data.velocity_y = event.data.flingStart.velocityY;
       scroll_state_data.is_in_inertial_phase = true;
       break;
     case WebInputEvent::GestureScrollUpdate:
       scroll_state_data.delta_x = -event.data.scrollUpdate.deltaX;
       scroll_state_data.delta_y = -event.data.scrollUpdate.deltaY;
       scroll_state_data.velocity_x = event.data.scrollUpdate.velocityX;
@@ skipping 1196 matching lines @@
   // is made asynchronously, to minimize divergence between main thread and
   // impl thread event handling paths.
   base::ThreadTaskRunnerHandle::Get()->PostTask(
       FROM_HERE,
       base::Bind(&InputScrollElasticityController::ObserveGestureEventAndResult,
                  scroll_elasticity_controller_->GetWeakPtr(), gesture_event,
                  scroll_result));
 }
 
 }  // namespace ui