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

ash/shelf/shelf_widget_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 "ash/shelf/shelf_widget.h"
 
 #include "ash/launcher/launcher.h"
 #include "ash/launcher/launcher_button.h"
 #include "ash/launcher/launcher_model.h"
 #include "ash/root_window_controller.h"
@@ skipping 36 matching lines @@
   ShelfWidget* shelf_widget = launcher->shelf_widget();
   EXPECT_FALSE(shelf_widget->CanActivate());
 
   shelf_widget->WillActivateAsFallback();
   EXPECT_TRUE(shelf_widget->CanActivate());
 
   wm::ActivateWindow(shelf_widget->GetNativeWindow());
   EXPECT_FALSE(shelf_widget->CanActivate());
 }
 
-void TestLauncherAlignment(aura::RootWindow* root,
+void TestLauncherAlignment(aura::Window* root,
                            ShelfAlignment alignment,
                            const std::string& expected) {
   Shell::GetInstance()->SetShelfAlignment(alignment, root);
   gfx::Screen* screen = gfx::Screen::GetScreenFor(root);
   EXPECT_EQ(expected,
             screen->GetDisplayNearestWindow(root).work_area().ToString());
 }
 
 TEST_F(ShelfWidgetTest, TestAlignment) {
   Launcher* launcher = Launcher::ForPrimaryDisplay();
@@ skipping 117 matching lines @@
   const int status_width =
       shelf->status_area_widget()->GetWindowBoundsInScreen().width();
   EXPECT_GT(status_width, 0);
   EXPECT_EQ(status_width,
             shelf->GetContentsView()->width() -
                 test::LauncherTestAPI(launcher).shelf_view()->width());
 }
 #endif
 
 }  // namespace ash