mus: Add a missing InitHost() call to fix a test.

services/ui/ws/window_manager_client_unittest.cc

Index: services/ui/ws/window_manager_client_unittest.cc
diff --git a/services/ui/ws/window_manager_client_unittest.cc b/services/ui/ws/window_manager_client_unittest.cc
index 0697239cfa0b7f2de3890ff73a3e1db538768805..67fcb63889a226c7e5386302df357a2048e4af42 100644
--- a/services/ui/ws/window_manager_client_unittest.cc
+++ b/services/ui/ws/window_manager_client_unittest.cc
@@ -730,6 +730,7 @@ TEST_F(WindowServerTest, OnWindowHierarchyChangedIncludesTransientParent) {
   aura::WindowTreeClient second_client(connector(), this);
   second_client.ConnectViaWindowTreeFactory();
   aura::WindowTreeHostMus window_tree_host_in_second_client(&second_client);
+  window_tree_host_in_second_client.InitHost();
   aura::Window* second_client_child = NewVisibleWindow(
       window_tree_host_in_second_client.window(), &second_client);
   std::unique_ptr<aura::WindowPortMus> window_port_mus =