Make GetRootWindow() return a Window instead of a RootWindow.

ash/wm/header_painter_unittest.cc

 // Copyright 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 "ash/wm/header_painter.h"
 
 #include "ash/ash_constants.h"
 #include "ash/root_window_settings.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 190 matching lines @@
     params.delegate = new ResizableWidgetDelegate(widget);
     params.type = Widget::InitParams::TYPE_WINDOW;
     widget->Init(params);
     return widget;
   }
 };
 
 TEST_F(HeaderPainterTest, CreateAndDeleteSingleWindow) {
   // Ensure that creating/deleting a window works well and doesn't cause
   // crashes.  See crbug.com/155634
-  aura::RootWindow* root = Shell::GetTargetRootWindow();
+  aura::Window* root = Shell::GetTargetRootWindow();
 
   scoped_ptr<Widget> widget(CreateTestWidget());
   scoped_ptr<HeaderPainter> painter(CreateTestPainter(widget.get()));
   widget->Show();
 
   // We only have one window, so it should use a solo header.
   EXPECT_TRUE(painter->UseSoloWindowHeader());
   EXPECT_TRUE(internal::GetRootWindowSettings(root)->solo_window_header);
 
   // Close the window.
@@ skipping 435 matching lines @@
   HeaderPainterOwner* o2 = new HeaderPainterOwner(w2);
   HeaderPainter* p2 = o2->header_painter();
   w2->Show();
   EXPECT_FALSE(p1->UseSoloWindowHeader());
   EXPECT_FALSE(p2->UseSoloWindowHeader());
 
   // Exit with no resource release. They'll be released at shutdown.
 }
 
 }  // namespace ash