Mus Demo: Demonstrate external window mode

services/ui/demo/mus_demo.cc

Index: services/ui/demo/mus_demo.cc
diff --git a/services/ui/demo/mus_demo.cc b/services/ui/demo/mus_demo.cc
index 04bc37b693525abd0aec432c1d128d8d2da8f989..9f9c6e8186e8c7b6e15e32a1a26c1a1e14aead60 100644
--- a/services/ui/demo/mus_demo.cc
+++ b/services/ui/demo/mus_demo.cc
@@ -72,6 +72,13 @@ MusDemo::WindowTreeData::WindowTreeData(
   Init(std::move(window_tree_host));
 }
 
+MusDemo::WindowTreeData::WindowTreeData(mojom::WindowTreeHostFactory* factory,
+                                        mojom::WindowTreeClientPtr tree_client,
+                                        int square_size)
+    : square_size_(square_size) {
+  factory->CreateWindowTreeHost(MakeRequest(&host_), std::move(tree_client));
+}
+
 MusDemo::WindowTreeData::~WindowTreeData() {}
 
 aura::Window* MusDemo::WindowTreeData::bitmap_window() {