Fixes bug in handling restacking because of transients

ui/aura/test/mus/test_window_tree.h

Index: ui/aura/test/mus/test_window_tree.h
diff --git a/ui/aura/test/mus/test_window_tree.h b/ui/aura/test/mus/test_window_tree.h
index 6b0995dcc97538696ffa27e6d3cd9c0d7cc08817..aff2967e2db17fa934190aa29471b991a0d2a9f4 100644
--- a/ui/aura/test/mus/test_window_tree.h
+++ b/ui/aura/test/mus/test_window_tree.h
@@ -26,6 +26,7 @@ enum class WindowTreeChangeType {
   NEW_WINDOW,
   PROPERTY,
   REMOVE_TRANSIENT,
+  REORDER,
   VISIBLE,
 
   // This covers all cases that aren't used in tests.
@@ -58,6 +59,8 @@ class TestWindowTree : public ui::mojom::WindowTree {
   // True if at least one function has been called that takes a change id.
   bool has_change() const { return !changes_.empty(); }
 
+  size_t number_of_changes() const { return changes_.size(); }
+
   // Acks all changes with a value of true.
   void AckAllChanges();