cc: Add SwapPromiseManager and SurfaceSequenceGenerator.

cc/trees/layer_tree.cc

Index: cc/trees/layer_tree.cc
diff --git a/cc/trees/layer_tree.cc b/cc/trees/layer_tree.cc
index cf0c3bc4760acdc50ee11f53511f2f8162d980bf..1ae0934bc42fd9c0a70868bea0eac1939f98fc18 100644
--- a/cc/trees/layer_tree.cc
+++ b/cc/trees/layer_tree.cc
@@ -720,4 +720,12 @@ void LayerTree::SetNeedsDisplayOnAllLayers() {
     layer->SetNeedsDisplay();
 }
 
+SwapPromiseManager* LayerTree::GetSwapPromiseManager() const {
+  return layer_tree_host_->GetSwapPromiseManager();
+}
+
+SurfaceSequenceGenerator* LayerTree::GetSurfaceSequenceGenerator() const {
+  return layer_tree_host_->GetSurfaceSequenceGenerator();
+}
+
 }  // namespace cc