List all child surfaces (including occluded) in CompositorFrame

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 596476081d1b175e64dcaf8246c6b47f83d837ad..06635e51f0d5776f8d1d4e5209779092cdc8c0c5 100644
--- a/cc/trees/layer_tree_impl.cc
+++ b/cc/trees/layer_tree_impl.cc
@@ -1319,6 +1319,19 @@ void LayerTreeImpl::RemoveLayerWithCopyOutputRequest(LayerImpl* layer) {
   }
 }
 
+void LayerTreeImpl::AddSurfaceLayer(LayerImpl* layer) {
+  DCHECK(std::find(surface_layers_.begin(), surface_layers_.end(), layer) ==
+         surface_layers_.end());
+  surface_layers_.push_back(layer);
+}
+
+void LayerTreeImpl::RemoveSurfaceLayer(LayerImpl* layer) {
+  std::vector<LayerImpl*>::iterator it =
+      std::find(surface_layers_.begin(), surface_layers_.end(), layer);
+  DCHECK(it != surface_layers_.end());
+  surface_layers_.erase(it);
+}
+
 const std::vector<LayerImpl*>& LayerTreeImpl::LayersWithCopyOutputRequest()
     const {
   // Only the active tree needs to know about layers with copy requests, as