Check WindowTreeClient for empty inflight queue upon teardown

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/mus/public/cpp/tests/test_window_tree_client_setup.h"
 
 #include "components/mus/public/cpp/tests/test_window_tree.h"
 #include "components/mus/public/cpp/tests/window_tree_client_private.h"
 #include "components/mus/public/cpp/window_tree_client.h"
 
@@ skipping 19 matching lines @@
   WindowTreeClientPrivate(window_tree_client_.get())
       .OnEmbed(window_tree_.get());
 }
 
 WindowTreeClient* TestWindowTreeClientSetup::window_tree_client() {
   return window_tree_client_.get();
 }
 
 void TestWindowTreeClientSetup::OnWillDestroyClient(
     mus::WindowTreeClient* client) {
+  // |window_tree_| stubs out the connection to the Mus Window Server. So we
+  // need to clear the client queue before tear down.
+  WindowTreeClientPrivate(window_tree_client_.get()).ClearInFlightQueue();
   // See comment in header as to why we do this.
   window_tree_client_.release();
 }
 
 }  // namespace mus