Make WindowTree::SetModal() take the type.

services/ui/ws/window_manager_state.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 "services/ui/ws/window_manager_state.h"
 
 #include <utility>
 
 #include "base/logging.h"
 #include "base/memory/weak_ptr.h"
@@ skipping 191 matching lines @@
 void WindowManagerState::CancelDragDrop() {
   event_dispatcher_.CancelDragDrop();
 }
 
 void WindowManagerState::EndDragDrop() {
   event_dispatcher_.EndDragDrop();
   UpdateNativeCursorFromDispatcher();
 }
 
 void WindowManagerState::AddSystemModalWindow(ServerWindow* window) {
-  DCHECK(!window->transient_parent());
   event_dispatcher_.AddSystemModalWindow(window);
 }
 
 const UserId& WindowManagerState::user_id() const {
   return window_tree_->user_id();
 }
 
 void WindowManagerState::OnWillDestroyTree(WindowTree* tree) {
   event_dispatcher_.OnWillDestroyDragTargetConnection(tree);
 
@@ skipping 447 matching lines @@
       window->RemoveObserver(this);
       orphaned_window_manager_display_roots_.erase(iter);
       return;
     }
   }
   NOTREACHED();
 }
 
 }  // namespace ws
 }  // namespace ui