aura-mus: Implement stacking in DesktopWindowTreeHostMus.

ui/views/mus/mus_client.cc

Index: ui/views/mus/mus_client.cc
diff --git a/ui/views/mus/mus_client.cc b/ui/views/mus/mus_client.cc
index 1ac3a789bc6bd5e1840f07b632a17958003253d3..93aed274f699db4c9906e74d38f4de1fe608dbf4 100644
--- a/ui/views/mus/mus_client.cc
+++ b/ui/views/mus/mus_client.cc
@@ -26,6 +26,7 @@
 #include "ui/views/mus/aura_init.h"
 #include "ui/views/mus/clipboard_mus.h"
 #include "ui/views/mus/desktop_window_tree_host_mus.h"
+#include "ui/views/mus/mus_client_test_observer.h"
 #include "ui/views/mus/pointer_watcher_event_router.h"
 #include "ui/views/mus/screen_mus.h"
 #include "ui/views/views_delegate.h"
@@ -62,7 +63,7 @@ MusClient::MusClient(service_manager::Connector* connector,
                      const service_manager::Identity& identity,
                      scoped_refptr<base::SingleThreadTaskRunner> io_task_runner,
                      bool create_wm_state)
-    : identity_(identity) {
+    : identity_(identity), test_observer_(nullptr) {
   DCHECK(!instance_);
   DCHECK(aura::Env::GetInstance());
   instance_ = this;
@@ -249,6 +250,11 @@ void MusClient::OnPointerEventObserved(const ui::PointerEvent& event,
   pointer_watcher_event_router_->OnPointerEventObserved(event, target);
 }
 
+void MusClient::OnChangeCompleted(aura::ChangeType type, bool success) {
+  if (test_observer_)
+    test_observer_->OnChangeCompleted(type, success);
+}
+
 void MusClient::OnWindowManagerFrameValuesChanged() {
   for (auto& observer : observer_list_)
     observer.OnWindowManagerFrameValuesChanged();