mus: Allow SetModal to fail gracefully

components/mus/public/cpp/lib/window_tree_client_impl.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/lib/window_tree_client_impl.h"
 
 #include <stddef.h>
 #include <utility>
 
 #include "base/bind.h"
@@ skipping 201 matching lines @@
   DCHECK(tree_);
   const uint32_t change_id =
       ScheduleInFlightChange(make_scoped_ptr(new CrashInFlightChange(
           window, ChangeType::REMOVE_TRANSIENT_WINDOW_FROM_PARENT)));
   tree_->RemoveTransientWindowFromParent(change_id, window->id());
 }
 
 void WindowTreeClientImpl::SetModal(Window* window) {
   DCHECK(tree_);
   const uint32_t change_id = ScheduleInFlightChange(
-      make_scoped_ptr(new CrashInFlightChange(window, ChangeType::SET_MODAL)));
+      make_scoped_ptr(new InFlightSetModalChange(window)));
   tree_->SetModal(change_id, window->id());
 }
 
 void WindowTreeClientImpl::Reorder(Window* window,
                                    Id relative_window_id,
                                    mojom::OrderDirection direction) {
   DCHECK(tree_);
   const uint32_t change_id = ScheduleInFlightChange(
       make_scoped_ptr(new CrashInFlightChange(window, ChangeType::REORDER)));
   tree_->ReorderWindow(change_id, window->id(), relative_window_id, direction);
@@ skipping 747 matching lines @@
 
 void WindowTreeClientImpl::SetUnderlaySurfaceOffsetAndExtendedHitArea(
     Window* window,
     const gfx::Vector2d& offset,
     const gfx::Insets& hit_area) {
   window_manager_internal_client_->SetUnderlaySurfaceOffsetAndExtendedHitArea(
       window->id(), offset.x(), offset.y(), mojo::Insets::From(hit_area));
 }
 
 }  // namespace mus