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 115 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, a GestureScrollBegin in the inertial phase indicates a fling
+      // start.
+      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;
       scroll_state_data.velocity_y = event.data.scrollUpdate.velocityY;
       scroll_state_data.is_in_inertial_phase =
           event.data.scrollUpdate.inertialPhase ==
           WebGestureEvent::MomentumPhase;
       break;
     case WebInputEvent::GestureScrollEnd:
     case WebInputEvent::GestureFlingCancel:
       scroll_state_data.is_ending = true;
+      scroll_state_data.may_precede_fling =
+          event.data.scrollEnd.mayPrecedeFling;
       break;
     default:
       NOTREACHED();
       break;
   }
   return cc::ScrollState(scroll_state_data);
 }
 
 void ReportInputEventLatencyUma(const WebInputEvent& event,
                                 const ui::LatencyInfo& latency_info) {
@@ skipping 517 matching lines @@
   if (!gesture_scroll_on_impl_thread_ && !gesture_pinch_on_impl_thread_)
     return DID_NOT_HANDLE;
 
   cc::ScrollState scroll_state = CreateScrollStateForGesture(gesture_event);
   gfx::Point scroll_point(gesture_event.x, gesture_event.y);
   gfx::Vector2dF scroll_delta(-gesture_event.data.scrollUpdate.deltaX,
                               -gesture_event.data.scrollUpdate.deltaY);
 
   if (ShouldAnimate(gesture_event.data.scrollUpdate.deltaUnits !=
                     blink::WebGestureEvent::ScrollUnits::Pixels)) {
+    DCHECK(!scroll_state.is_in_inertial_phase());
     base::TimeTicks event_time =
         base::TimeTicks() +
         base::TimeDelta::FromSecondsD(gesture_event.timeStampSeconds);
     base::TimeDelta delay = base::TimeTicks::Now() - event_time;
     switch (input_handler_->ScrollAnimated(scroll_point, scroll_delta, delay)
                 .thread) {
       case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
         return DID_HANDLE;
       case cc::InputHandler::SCROLL_IGNORED:
         return DROP_EVENT;
@@ skipping 715 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