Touchpad scroll latching enabled for Mac behind flag.

cc/trees/layer_tree_host_impl.cc

 // Copyright 2011 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 "cc/trees/layer_tree_host_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 2707 matching lines @@
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::ScrollBegin(
     ScrollState* scroll_state,
     InputHandler::ScrollInputType type) {
   ScrollStatus scroll_status;
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   TRACE_EVENT0("cc", "LayerTreeHostImpl::ScrollBegin");
 
+  // On Mac a scroll begin with |inertial_phase| = true happens to handle a
+  // fling.
+  if (scroll_state->is_in_inertial_phase())
+    return FlingScrollBegin();
+
   ClearCurrentlyScrollingLayer();
 
   gfx::Point viewport_point(scroll_state->position_x(),
                             scroll_state->position_y());
 
   gfx::PointF device_viewport_point = gfx::ScalePoint(
       gfx::PointF(viewport_point), active_tree_->device_scale_factor());
   LayerImpl* layer_impl =
       active_tree_->FindLayerThatIsHitByPoint(device_viewport_point);
 
@@ skipping 142 matching lines @@
       scroll_status.thread = SCROLL_IGNORED;
       scroll_status.main_thread_scrolling_reasons =
           MainThreadScrollingReason::kNotScrollable;
     }
     return scroll_status;
   }
 
   ScrollStateData scroll_state_data;
   scroll_state_data.position_x = viewport_point.x();
   scroll_state_data.position_y = viewport_point.y();
-  scroll_state_data.is_in_inertial_phase = true;
+  scroll_state_data.is_in_inertial_phase = false;
   ScrollState scroll_state(scroll_state_data);
 
   // ScrollAnimated is used for animated wheel scrolls. We find the first layer
   // that can scroll and set up an animation of its scroll offset. Note that
   // this does not currently go through the scroll customization machinery
   // that ScrollBy uses for non-animated wheel scrolls.
   scroll_status = ScrollBegin(&scroll_state, WHEEL);
   scroll_node = scroll_tree.CurrentlyScrollingNode();
   if (scroll_status.thread == SCROLL_ON_IMPL_THREAD) {
     gfx::Vector2dF pending_delta = scroll_delta;
@@ skipping 17 matching lines @@
         gfx::Vector2dF scroll_delta =
             ComputeScrollDelta(scroll_node, pending_delta);
         if (ScrollAnimationCreate(scroll_node, scroll_delta))
           return scroll_status;
 
         pending_delta -= scroll_delta;
       }
     }
   }
   scroll_state.set_is_ending(true);
+  // TODO(Sahel): Once the touchpad scroll latching for Non-mac devices is
+  // impelemented, the current scrolling layer should not get cleared after
+  // each animation (crbug.com/526463).
   ScrollEnd(&scroll_state);
+  ClearCurrentlyScrollingLayer();
+
   return scroll_status;
 }
 
 gfx::Vector2dF LayerTreeHostImpl::ScrollNodeWithViewportSpaceDelta(
     ScrollNode* scroll_node,
     const gfx::PointF& viewport_point,
     const gfx::Vector2dF& viewport_delta,
     ScrollTree* scroll_tree) {
   // Layers with non-invertible screen space transforms should not have passed
   // the scroll hit test in the first place.
@@ skipping 333 matching lines @@
   scroll_affects_scroll_handler_ = false;
   accumulated_root_overscroll_ = gfx::Vector2dF();
 }
 
 void LayerTreeHostImpl::ScrollEnd(ScrollState* scroll_state) {
   DCHECK(scroll_state);
   DCHECK(scroll_state->delta_x() == 0 && scroll_state->delta_y() == 0);
 
   DistributeScrollDelta(scroll_state);
   top_controls_manager_->ScrollEnd();
-  ClearCurrentlyScrollingLayer();
+
+  if (scroll_state->is_in_inertial_phase()) {
+    // Only clear the currently scrolling layer if we know the scroll is done.
+    // A non-inertial scroll end could be followed by an inertial scroll.
+    ClearCurrentlyScrollingLayer();
+  }
 }
 
 InputHandler::ScrollStatus LayerTreeHostImpl::FlingScrollBegin() {
   InputHandler::ScrollStatus scroll_status;
   scroll_status.main_thread_scrolling_reasons =
       MainThreadScrollingReason::kNotScrollingOnMain;
   if (!CurrentlyScrollingLayer()) {
     scroll_status.thread = SCROLL_IGNORED;
     scroll_status.main_thread_scrolling_reasons =
         MainThreadScrollingReason::kNoScrollingLayer;
@@ skipping 793 matching lines @@
         layer->OnFilterIsCurrentlyAnimatingChanged(is_animating);
         break;
     }
   }
 }
 
 void LayerTreeHostImpl::ScrollOffsetAnimationFinished() {
   // TODO(majidvp): We should pass in the original starting scroll position here
   ScrollStateData scroll_state_data;
   ScrollState scroll_state(scroll_state_data);
+  // TODO(Sahel): Once the touchpad scroll latching for Non-mac devices is
+  // impelemented, the current scrolling layer should not get cleared after
+  // each animation (crbug.com/526463).
   ScrollEnd(&scroll_state);
+  ClearCurrentlyScrollingLayer();
 }
 
 gfx::ScrollOffset LayerTreeHostImpl::GetScrollOffsetForAnimation(
     ElementId element_id) const {
   if (active_tree()) {
     LayerImpl* layer = active_tree()->LayerByElementId(element_id);
     if (layer)
       return layer->ScrollOffsetForAnimation();
   }
 
   return gfx::ScrollOffset();
 }
 
 bool LayerTreeHostImpl::SupportsImplScrolling() const {
   // Supported in threaded mode.
   return task_runner_provider_->HasImplThread();
 }
 
 bool LayerTreeHostImpl::CommitToActiveTree() const {
   // In single threaded mode we skip the pending tree and commit directly to the
   // active tree.
   return !task_runner_provider_->HasImplThread();
 }
 
 }  // namespace cc