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 7282f52b671098bc8f561d2dc3f5c34a3875ab5d..51e58a579350f9c08076cee812e2b36ae83d1f01 100644
--- a/cc/trees/layer_tree.cc
+++ b/cc/trees/layer_tree.cc
@@ -728,4 +728,12 @@ const LayerTreeSettings& LayerTree::GetSettings() const {
   return layer_tree_host_->GetSettings();
 }
 
+SwapPromiseManager* LayerTree::GetSwapPromiseManager() const {
+  return layer_tree_host_->GetSwapPromiseManager();
+}
+
+SurfaceSequenceGenerator* LayerTree::GetSurfaceSequenceGenerator() const {
+  return layer_tree_host_->GetSurfaceSequenceGenerator();
+}
+
 }  // namespace cc