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

ash/wm/system_modal_container_layout_manager_unittest.cc

 // Copyright (c) 2012 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/system_modal_container_layout_manager.h"
 
 #include "ash/root_window_controller.h"
 #include "ash/session_state_delegate.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
@@ skipping 72 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(TestWindow);
 };
 
 class EventTestWindow : public TestWindow {
  public:
   explicit EventTestWindow(bool modal) : TestWindow(modal),
                                          mouse_presses_(0) {}
   virtual ~EventTestWindow() {}
 
-  aura::Window* OpenTestWindowWithContext(aura::RootWindow* context) {
+  aura::Window* OpenTestWindowWithContext(aura::Window* context) {
     views::Widget* widget =
         views::Widget::CreateWindowWithContext(this, context);
     widget->Show();
     return widget->GetNativeView();
   }
 
   aura::Window* OpenTestWindowWithParent(aura::Window* parent) {
     DCHECK(parent);
     views::Widget* widget =
         views::Widget::CreateWindowWithParent(this, parent);
@@ skipping 382 matching lines @@
 
   // No more modal screen.
   modal1->Hide();
   TestWindow::CloseTestWindow(modal1.release());
   EXPECT_FALSE(AllRootWindowsHaveModalBackgrounds());
   EXPECT_TRUE(wm::IsActiveWindow(normal.get()));
 }
 
 }  // namespace test
 }  // namespace ash