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

cc/trees/layer_tree_impl.cc

Index: cc/trees/layer_tree_impl.cc
diff --git a/cc/trees/layer_tree_impl.cc b/cc/trees/layer_tree_impl.cc
index dc9b4e9bfce64176681353802396ee24b174597e..e5c95593eba119c7e507d2bf274bcf7a78409423 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -261,8 +261,9 @@ void LayerTreeImpl::UpdateScrollbars(int scroll_layer_id, int clip_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 {
@@ -1059,8 +1060,7 @@ bool LayerTreeImpl::UpdateDrawProperties(bool update_lcd_text) {
     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);