mus: Unset the cursor client during teardown.

ui/views/mus/desktop_window_tree_host_mus.cc

Index: ui/views/mus/desktop_window_tree_host_mus.cc
diff --git a/ui/views/mus/desktop_window_tree_host_mus.cc b/ui/views/mus/desktop_window_tree_host_mus.cc
index c3097bd499666b4fe677a99dc499a001b7568652..8b131ee80c154ac3f8e09667fc64d36b90d69af3 100644
--- a/ui/views/mus/desktop_window_tree_host_mus.cc
+++ b/ui/views/mus/desktop_window_tree_host_mus.cc
@@ -190,6 +190,10 @@ DesktopWindowTreeHostMus::DesktopWindowTreeHostMus(
 }
 
 DesktopWindowTreeHostMus::~DesktopWindowTreeHostMus() {
+  // The cursor-client can be accessed during WindowTreeHostMus tear-down. So
+  // the cursor-client needs to be unset on the root-window before
+  // |cursor_manager_| is destroyed.
+  aura::client::SetCursorClient(window(), nullptr);
   MusClient::Get()->RemoveObserver(this);
   aura::Env::GetInstance()->RemoveObserver(this);
   desktop_native_widget_aura_->OnDesktopWindowTreeHostDestroyed(this);