Keeping track of descendants that draw content instead of recalcualting

cc/test/fake_layer_tree_host_impl.cc

Index: cc/test/fake_layer_tree_host_impl.cc
diff --git a/cc/test/fake_layer_tree_host_impl.cc b/cc/test/fake_layer_tree_host_impl.cc
index 7361794e7b1aa707018c8fe3a0f6214f5863ada6..b91aee38daf9dc3aa0c9554eef8653cbcce99e48 100644
--- a/cc/test/fake_layer_tree_host_impl.cc
+++ b/cc/test/fake_layer_tree_host_impl.cc
@@ -54,4 +54,25 @@ void FakeLayerTreeHostImpl::SetCurrentFrameTimeTicks(
   current_frame_time_ticks_ = current_frame_time_ticks;
 }
 
+int FakeLayerTreeHostImpl::RecursiveUpdateNumChildren(LayerImpl* layer) {
+  int num_children_that_draw_content = 0;
+  for (size_t i = 0; i < layer->children().size(); ++i) {
+    num_children_that_draw_content +=
+        RecursiveUpdateNumChildren(layer->children()[i]);
+  }
+  layer->SetNumDescendantsThatDrawContent(num_children_that_draw_content);
+  return num_children_that_draw_content + (layer->DrawsContent() ? 1 : 0) +
+         (layer->HasDelegatedContent() ? 1000 : 0);
+}
+
+void FakeLayerTreeHostImpl::UpdateDrawProperties() {
+  FakeSyncDrawProperties(active_tree());
+  active_tree()->UpdateDrawProperties();
+}
+
+void FakeLayerTreeHostImpl::FakeSyncDrawProperties(LayerTreeImpl* layerTree) {
+  RecursiveUpdateNumChildren(layerTree->root_layer());
+  layerTree->UpdateDrawProperties();
+}
+
 }  // namespace cc