Check WindowTreeClient for empty inflight queue upon teardown

components/mus/public/cpp/lib/window_tree_client.cc

 // Copyright 2014 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/window_tree_client.h"
 
 #include <stddef.h>
 
 #include <string>
 #include <utility>
@@ skipping 113 matching lines @@
   // exception is the window manager and embed roots, which may know about
   // other random windows that it doesn't own.
   // NOTE: we manually delete as we're a friend.
   while (!tracker.windows().empty())
     delete tracker.windows().front();
 
   FOR_EACH_OBSERVER(WindowTreeClientObserver, observers_,
                     OnWillDestroyClient(this));
 
   delegate_->OnWindowTreeClientDestroyed(this);
+
+  DCHECK(in_flight_map_.empty());
 }
 
 void WindowTreeClient::ConnectViaWindowTreeFactory(
     shell::Connector* connector) {
   // Clients created with no root shouldn't delete automatically.
   delete_on_no_roots_ = false;
 
   // The client id doesn't really matter, we use 101 purely for debugging.
   client_id_ = 101;
 
@@ skipping 958 matching lines @@
     Window* window,
     const gfx::Vector2d& offset,
     const gfx::Insets& hit_area) {
   if (window_manager_internal_client_) {
     window_manager_internal_client_->SetUnderlaySurfaceOffsetAndExtendedHitArea(
         server_id(window), offset.x(), offset.y(), hit_area);
   }
 }
 
 }  // namespace mus