Do SetNeedsCommit() instead of Composite() in threaded mode.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index dfe46589a2942643d88707dcb0a00c01cf8af263..c83a68e4a7ec9e6ddbcc552b1d90d8f40019099c 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -696,11 +696,9 @@ void LayerTreeHost::NotifyInputThrottledUntilCommit() {
 }
 
 void LayerTreeHost::Composite(base::TimeTicks frame_begin_time) {
-  if (!proxy_->HasImplThread())
-    static_cast<SingleThreadProxy*>(proxy_.get())->CompositeImmediately(
-        frame_begin_time);
-  else
-    SetNeedsCommit();
+  DCHECK(!proxy_->HasImplThread());
+  SingleThreadProxy* proxy = static_cast<SingleThreadProxy*>(proxy_.get());
+  proxy->CompositeImmediately(frame_begin_time);
 }
 
 bool LayerTreeHost::InitializeOutputSurfaceIfNeeded() {