mash: Reverse the responsibilities of the NewWindowClient.

ash/common/test/wm_shell_test_api.cc

Index: ash/common/test/wm_shell_test_api.cc
diff --git a/ash/common/test/wm_shell_test_api.cc b/ash/common/test/wm_shell_test_api.cc
index fc37d56bd9d6eea36f82b8dd985ba8c757e41b93..6be4bab01a1da82d638b76afee3eaa35be66c5a4 100644
--- a/ash/common/test/wm_shell_test_api.cc
+++ b/ash/common/test/wm_shell_test_api.cc
@@ -21,9 +21,4 @@ void WmShellTestApi::SetSystemTrayDelegate(
   WmShell::Get()->SetSystemTrayDelegate(std::move(delegate));
 }
 
-void WmShellTestApi::SetNewWindowClient(
-    std::unique_ptr<mojom::NewWindowClient> client) {
-  WmShell::Get()->new_window_client_ = std::move(client);
-}
-
 }  // namespace ash