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 114 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;
@@ skipping 338 matching lines @@
           : 0);
 
   if (wheel_event.scrollByPage) {
     // TODO(jamesr): We don't properly handle scroll by page in the compositor
     // thread, so punt it to the main thread. http://crbug.com/236639
     result = DID_NOT_HANDLE;
     RecordMainThreadScrollingReasons(
         blink::WebGestureDeviceTouchpad,
         cc::MainThreadScrollingReason::kPageBasedScrolling);
 
-  } else if (ShouldAnimate(wheel_event.hasPreciseScrollingDeltas)) {
-    cc::InputHandler::ScrollStatus scroll_status =
-        input_handler_->ScrollAnimated(gfx::Point(wheel_event.x, wheel_event.y),
-                                       scroll_delta);
-
-    RecordMainThreadScrollingReasons(
-        blink::WebGestureDeviceTouchpad,
-        scroll_status.main_thread_scrolling_reasons);
-
-    switch (scroll_status.thread) {
-      case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
-        result = DID_HANDLE;
-        break;
-      case cc::InputHandler::SCROLL_IGNORED:
-        result = DROP_EVENT;
-        break;
-      default:
-        result = DID_NOT_HANDLE;
-        break;
-    }
   } else {
+    DCHECK(!ShouldAnimate(wheel_event.hasPreciseScrollingDeltas));
     cc::ScrollStateData scroll_state_begin_data;
     scroll_state_begin_data.position_x = wheel_event.x;
     scroll_state_begin_data.position_y = wheel_event.y;
     scroll_state_begin_data.is_beginning = true;
     cc::ScrollState scroll_state_begin(scroll_state_begin_data);
     cc::InputHandler::ScrollStatus scroll_status = input_handler_->ScrollBegin(
         &scroll_state_begin, cc::InputHandler::WHEEL);
 
     RecordMainThreadScrollingReasons(
         blink::WebGestureDeviceTouchpad,
@@ skipping 108 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());
     switch (input_handler_->ScrollAnimated(scroll_point, scroll_delta).thread) {
       case cc::InputHandler::SCROLL_ON_IMPL_THREAD:
         return DID_HANDLE;
       case cc::InputHandler::SCROLL_IGNORED:
         return DROP_EVENT;
       default:
         return DID_NOT_HANDLE;
     }
   }
   cc::InputHandlerScrollResult scroll_result =
@@ skipping 689 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