views/mus: Add support for child widgets.

ui/views/controls/native/native_view_host_aura_unittest.cc

 // Copyright (c) 2013 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/controls/native/native_view_host_aura.h"
 
 #include <memory>
 
 #include "base/macros.h"
 #include "ui/aura/client/aura_constants.h"
@@ skipping 239 matching lines @@
             clipping_window()->bounds().ToString());
 
   DestroyHost();
 }
 
 // Ensure native view is parented to the root window after detaching. This is
 // a regression test for http://crbug.com/389261.
 TEST_F(NativeViewHostAuraTest, ParentAfterDetach) {
   CreateHost();
   aura::Window* child_win = child()->GetNativeView();
-  aura::Window* root_window = child_win->GetRootWindow();
-  aura::WindowTreeHost* child_win_tree_host = child_win->GetHost();
 
   NativeViewHostWindowObserver test_observer;
   child_win->AddObserver(&test_observer);
 
   host()->Detach();
-  EXPECT_EQ(root_window, child_win->GetRootWindow());
-  EXPECT_EQ(child_win_tree_host, child_win->GetHost());
+  EXPECT_EQ(nullptr, child_win->GetRootWindow());
+  EXPECT_EQ(nullptr, child_win->GetHost());
 
   DestroyHost();
 
   // The window is detached, so no longer associated with any Widget hierarchy.
   // The root window still owns it, but the test harness checks for orphaned
   // windows during TearDown().
   DestroyTopLevel();
   EXPECT_EQ(0u, test_observer.events().size());
   delete child_win;
   ASSERT_EQ(1u, test_observer.events().size());
@@ skipping 84 matching lines @@
 
   host()->SetVisible(false);
   EXPECT_FALSE(clipping_window()->IsVisible());
   EXPECT_FALSE(child()->IsVisible());
 
   DestroyHost();
   DestroyTopLevel();
 }
 
 }  // namespace views