Refactor scroll chaining to use ScrollNodes without going through LayerImpl

cc/input/scroll_state.cc

 // Copyright 2015 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/input/scroll_state.h"
 
 #include <utility>
 
 #include "cc/trees/layer_tree_impl.h"
 #include "cc/trees/scroll_node.h"
@@ skipping 10 matching lines @@
 void ScrollState::ConsumeDelta(double x, double y) {
   data_.delta_x -= x;
   data_.delta_y -= y;
 
   if (x || y)
     data_.delta_consumed_for_scroll_sequence = true;
 }
 
 void ScrollState::DistributeToScrollChainDescendant() {
   if (!scroll_chain_.empty()) {
-    const ScrollNode* next = scroll_chain_.front();
+    ScrollNode* next = scroll_chain_.front();
     scroll_chain_.pop_front();
-    layer_tree_impl_->LayerById(next->owning_layer_id)->DistributeScroll(this);
+
+    ScrollTree& scroll_tree = layer_tree_impl_->property_trees()->scroll_tree;
+    scroll_tree.DistributeScroll(next, this);
   }
 }
 
 }  // namespace cc