cc: Construct the RSLL 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 1742 matching lines @@
 
     if (!state->closest_match || in_front_of_previous_candidate) {
       state->closest_distance = distance_to_intersection;
       state->closest_match = layer;
     }
   }
 }
 
 static bool ScrollsOrScrollbarAnyDrawnRenderSurfaceLayerListMember(
     LayerImpl* layer) {
-  if (!layer->scrollable() && !layer->ToScrollbarLayer())
-    return false;
-  if (layer->layer_or_descendant_is_drawn())
-    return true;
-
-  if (!layer->scroll_children())
-    return false;
-  for (std::set<LayerImpl*>::const_iterator it =
-           layer->scroll_children()->begin();
-       it != layer->scroll_children()->end(); ++it) {
-    if ((*it)->layer_or_descendant_is_drawn())
-      return true;
-  }
-  return false;
+  return layer->scrolls_drawn_descendant() ||
+         (layer->ToScrollbarLayer() &&
+          layer->IsDrawnRenderSurfaceLayerListMember());
 }
 
 struct FindScrollingLayerOrScrollbarLayerFunctor {
   bool operator()(LayerImpl* layer) const {
     return ScrollsOrScrollbarAnyDrawnRenderSurfaceLayerListMember(layer);
   }
 };
 
 LayerImpl*
 LayerTreeImpl::FindFirstScrollingLayerOrScrollbarLayerThatIsHitByPoint(
@@ skipping 321 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