Makes DesktopWindowTreeHostMus call OnNativeWidgetCreated()

ui/views/mus/desktop_window_tree_host_mus.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 "ui/views/mus/desktop_window_tree_host_mus.h"
 
 #include "base/memory/ptr_util.h"
 #include "ui/aura/client/aura_constants.h"
 #include "ui/aura/client/drag_drop_client.h"
 #include "ui/aura/client/focus_client.h"
@@ skipping 27 matching lines @@
 
 bool DesktopWindowTreeHostMus::IsDocked() const {
   return window()->GetProperty(aura::client::kShowStateKey) ==
          ui::SHOW_STATE_DOCKED;
 }
 
 void DesktopWindowTreeHostMus::Init(aura::Window* content_window,
                                     const Widget::InitParams& params) {}
 
 void DesktopWindowTreeHostMus::OnNativeWidgetCreated(
-    const Widget::InitParams& params) {}
+    const Widget::InitParams& params) {
+  native_widget_delegate_->OnNativeWidgetCreated(true);
+}
 
 std::unique_ptr<corewm::Tooltip> DesktopWindowTreeHostMus::CreateTooltip() {
   return base::MakeUnique<corewm::TooltipAura>();
 }
 
 std::unique_ptr<aura::client::DragDropClient>
 DesktopWindowTreeHostMus::CreateDragDropClient(
     DesktopNativeCursorManager* cursor_manager) {
   // aura-mus handles installing a DragDropClient.
   return nullptr;
@@ skipping 275 matching lines @@
   Widget* widget = native_widget_delegate_->AsWidget();
   window()->SetProperty(aura::client::kCanMaximizeKey,
                         widget->widget_delegate()->CanMaximize());
   window()->SetProperty(aura::client::kCanMinimizeKey,
                         widget->widget_delegate()->CanMinimize());
   window()->SetProperty(aura::client::kCanResizeKey,
                         widget->widget_delegate()->CanResize());
 }
 
 }  // namespace views