Add SwapPromise support to LayerTreeHost and LayerTreeImpl

cc/test/layer_tree_test.cc

Index: cc/test/layer_tree_test.cc
diff --git a/cc/test/layer_tree_test.cc b/cc/test/layer_tree_test.cc
index 1437f2ccc08a4b1cb99dd952cd3fbfef28cd8cde..d4cf5b82abdc99a8d1e8dcbe901d921e38feec1c 100644
--- a/cc/test/layer_tree_test.cc
+++ b/cc/test/layer_tree_test.cc
@@ -393,6 +393,13 @@ void LayerTreeTest::PostSetNeedsCommitToMainThread() {
                                          main_thread_weak_ptr_));
 }
 
+void LayerTreeTest::PostSetNeedsUpdateLayersToMainThread() {
+  main_task_runner_->PostTask(
+      FROM_HERE,
+      base::Bind(&LayerTreeTest::DispatchSetNeedsUpdateLayers,
+                 main_thread_weak_ptr_));
+}
+
 void LayerTreeTest::PostReadbackToMainThread() {
   main_task_runner_->PostTask(
       FROM_HERE,
@@ -534,6 +541,13 @@ void LayerTreeTest::DispatchSetNeedsCommit() {
     layer_tree_host_->SetNeedsCommit();
 }
 
+void LayerTreeTest::DispatchSetNeedsUpdateLayers() {
+  DCHECK(!proxy() || proxy()->IsMainThread());
+
+  if (layer_tree_host_)
+    layer_tree_host_->SetNeedsUpdateLayers();
+}
+
 void LayerTreeTest::DispatchReadback() {
   DCHECK(!proxy() || proxy()->IsMainThread());