Refactor scroll chaining to use ScrollNodes without going through LayerImpl

cc/input/scroll_state.h

 // 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.
 
 #ifndef CC_INPUT_SCROLL_STATE_H_
 #define CC_INPUT_SCROLL_STATE_H_
 
 #include <list>
 #include <memory>
 
@@ skipping 43 matching lines @@
   void set_is_ending(bool is_ending) { data_.is_ending = is_ending; }
 
   // True if this scroll is allowed to bubble upwards.
   bool should_propagate() const { return data_.should_propagate; }
   // True if the user interacts directly with the screen, e.g., via touch.
   bool is_direct_manipulation() const { return data_.is_direct_manipulation; }
   void set_is_direct_manipulation(bool is_direct_manipulation) {
     data_.is_direct_manipulation = is_direct_manipulation;
   }
 
-  void set_scroll_chain_and_layer_tree(
-      const std::list<const ScrollNode*>& scroll_chain,
-      LayerTreeImpl* layer_tree_impl) {
+  void set_scroll_chain_and_layer_tree(std::list<ScrollNode*>* scroll_chain,

[bokan, 2017/02/21 19:33:39]

Nit, why pass by pointer rather than const-ref?

[pdr., 2017/02/22 21:35:59]

Good catch, this was just a mistake. I started removing consts and got carried
away. Fix up: https://codereview.chromium.org/2713713002

+                                       LayerTreeImpl* layer_tree_impl) {
     layer_tree_impl_ = layer_tree_impl;
-    scroll_chain_ = scroll_chain;
+    scroll_chain_ = *scroll_chain;
   }
 
   void set_current_native_scrolling_node(ScrollNode* scroll_node) {
     data_.set_current_native_scrolling_node(scroll_node);
   }
 
   ScrollNode* current_native_scrolling_node() const {
     return data_.current_native_scrolling_node();
   }
 
@@ skipping 13 matching lines @@
 
   bool caused_scroll_x() const { return data_.caused_scroll_x; }
   bool caused_scroll_y() const { return data_.caused_scroll_y; }
 
   LayerTreeImpl* layer_tree_impl() { return layer_tree_impl_; }
   ScrollStateData* data() { return &data_; }
 
  private:
   ScrollStateData data_;
   LayerTreeImpl* layer_tree_impl_;
-  std::list<const ScrollNode*> scroll_chain_;
+  std::list<ScrollNode*> scroll_chain_;
 };
 
 }  // namespace cc
 
 #endif  // CC_INPUT_SCROLL_STATE_H_