Replace three callsites to LayerImpl::GetRenderSurface with effect tree calls.

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 243 matching lines @@
       scrollbar->SetScrollLayerLength(scroll_size.height());
     }
     scrollbar->SetVerticalAdjust(clip_layer->ViewportBoundsDelta().y());
   }
 
   if (y_offset_did_change && IsViewportLayerId(scroll_layer_id))
     TRACE_COUNTER_ID1("cc", "scroll_offset_y", scroll_layer->id(),
                       current_offset.y());
 }
 
-RenderSurfaceImpl* LayerTreeImpl::RootRenderSurface() const {
-  return layer_list_.empty() ? nullptr : layer_list_[0]->GetRenderSurface();
+const RenderSurfaceImpl* LayerTreeImpl::RootRenderSurface() const {
+  return property_trees_.effect_tree.GetRenderSurface(
+      EffectTree::kContentsRootNodeId);
 }
 
 bool LayerTreeImpl::LayerListIsEmpty() const {
   return layer_list_.empty();
 }
 
 void LayerTreeImpl::SetRootLayerForTesting(std::unique_ptr<LayerImpl> layer) {
   if (root_layer_for_testing_ && layer.get() != root_layer_for_testing_)
     RemoveLayer(root_layer_for_testing_->id());
   root_layer_for_testing_ = layer.get();
@@ skipping 776 matching lines @@
       UMA_HISTOGRAM_COUNTS_100(
           base::StringPrintf("Compositing.%s.NumRenderSurfaces", client_name),
           base::saturated_cast<int>(render_surface_list_.size()));
     }
   }
 
   {
     TRACE_EVENT2("cc", "LayerTreeImpl::UpdateDrawProperties::Occlusion",
                  "IsActive", IsActiveTree(), "SourceFrameNumber",
                  source_frame_number_);
-    OcclusionTracker occlusion_tracker(
-        layer_list_[0]->GetRenderSurface()->content_rect());
+    OcclusionTracker occlusion_tracker(RootRenderSurface()->content_rect());
     occlusion_tracker.set_minimum_tracking_size(
         settings().minimum_occlusion_tracking_size);
 
     for (EffectTreeLayerListIterator it(this);
          it.state() != EffectTreeLayerListIterator::State::END; ++it) {
       occlusion_tracker.EnterLayer(it);
 
       if (it.state() == EffectTreeLayerListIterator::State::LAYER) {
         LayerImpl* layer = it.current_layer();
         layer->draw_properties().occlusion_in_content_space =
@@ skipping 1046 matching lines @@
 
 void LayerTreeImpl::ResetAllChangeTracking() {
   layers_that_should_push_properties_.clear();
   // Iterate over all layers, including masks.
   for (auto& layer : *layers_)
     layer->ResetChangeTracking();
   property_trees_.ResetAllChangeTracking();
 }
 
 }  // namespace cc