cc : Calculate jitter without using layer hierarchy

cc/trees/layer_tree_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_impl.h"
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include <algorithm>
@@ skipping 43 matching lines @@
     scoped_refptr<SyncedProperty<ScaleGroup>> page_scale_factor,
     scoped_refptr<SyncedTopControls> top_controls_shown_ratio,
     scoped_refptr<SyncedElasticOverscroll> elastic_overscroll)
     : layer_tree_host_impl_(layer_tree_host_impl),
       source_frame_number_(-1),
       is_first_frame_after_commit_tracker_(-1),
       root_layer_(nullptr),
       hud_layer_(nullptr),
       background_color_(0),
       has_transparent_background_(false),
-      last_scrolled_layer_id_(Layer::INVALID_ID),
+      last_scrolled_scroll_node_id_(Layer::INVALID_ID),
       overscroll_elasticity_layer_id_(Layer::INVALID_ID),
       page_scale_layer_id_(Layer::INVALID_ID),
       inner_viewport_scroll_layer_id_(Layer::INVALID_ID),
       outer_viewport_scroll_layer_id_(Layer::INVALID_ID),
       page_scale_factor_(page_scale_factor),
       min_page_scale_factor_(0),
       max_page_scale_factor_(0),
       device_scale_factor_(1.f),
       painted_device_scale_factor_(1.f),
       elastic_overscroll_(elastic_overscroll),
@@ skipping 433 matching lines @@
              : NULL;
 }
 
 LayerImpl* LayerTreeImpl::CurrentlyScrollingLayer() const {
   DCHECK(IsActiveTree());
   const ScrollNode* scroll_node =
       property_trees_.scroll_tree.CurrentlyScrollingNode();
   return LayerById(scroll_node ? scroll_node->owner_id : Layer::INVALID_ID);
 }
 
-int LayerTreeImpl::LastScrolledLayerId() const {
-  return last_scrolled_layer_id_;
+int LayerTreeImpl::LastScrolledScrollNodeId() const {
+  return last_scrolled_scroll_node_id_;
 }
 
 void LayerTreeImpl::SetCurrentlyScrollingLayer(LayerImpl* layer) {
   ScrollTree& scroll_tree = property_trees()->scroll_tree;
   ScrollNode* scroll_node = scroll_tree.CurrentlyScrollingNode();
   int old_id = scroll_node ? scroll_node->owner_id : Layer::INVALID_ID;
   int new_id = layer ? layer->id() : Layer::INVALID_ID;
   int new_scroll_node_id = layer ? layer->scroll_tree_index() : -1;
   if (layer)
-    last_scrolled_layer_id_ = new_id;
+    last_scrolled_scroll_node_id_ = new_scroll_node_id;
 
   if (old_id == new_id)
     return;
 
   ScrollbarAnimationController* old_animation_controller =
       layer_tree_host_impl_->ScrollbarAnimationControllerForId(old_id);
   ScrollbarAnimationController* new_animation_controller =
       layer_tree_host_impl_->ScrollbarAnimationControllerForId(new_id);
 
   if (old_animation_controller)
@@ skipping 1566 matching lines @@
 }
 
 void LayerTreeImpl::ResetAllChangeTracking(PropertyTrees::ResetFlags flag) {
   layers_that_should_push_properties_.clear();
   for (auto* layer : *this)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking(flag);
 }
 
 }  // namespace cc