Check WindowTreeClient for empty inflight queue upon teardown

components/mus/public/cpp/tests/window_tree_client_private.cc

Index: components/mus/public/cpp/tests/window_tree_client_private.cc
diff --git a/components/mus/public/cpp/tests/window_tree_client_private.cc b/components/mus/public/cpp/tests/window_tree_client_private.cc
index 3d2e2bd5e92dfc1d2bb52ca73348ca4057bbaf50..cb923d4aa06afb8d1cf8b131e38f1f6c27d7ea20 100644
--- a/components/mus/public/cpp/tests/window_tree_client_private.cc
+++ b/components/mus/public/cpp/tests/window_tree_client_private.cc
@@ -4,6 +4,8 @@
 
 #include "components/mus/public/cpp/tests/window_tree_client_private.h"
 
+#include "base/run_loop.h"
+#include "components/mus/public/cpp/lib/in_flight_change.h"
 #include "components/mus/public/cpp/window.h"
 #include "components/mus/public/cpp/window_tree_client.h"
 
@@ -43,4 +45,15 @@ void WindowTreeClientPrivate::CallOnWindowInputEvent(
                                         std::move(event), observer_id);
 }
 
+void WindowTreeClientPrivate::ClearInFlightQueue() {
+  tree_client_impl_->in_flight_map_.clear();
+}
+
+void WindowTreeClientPrivate::WaitForInFlightQueue() {
+  while (!tree_client_impl_->in_flight_map_.empty()) {
+    base::RunLoop run_loop;
+    run_loop.RunUntilIdle();
+  }
+}
+
 }  // namespace mus