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

ash/wm/panels/panel_layout_manager_unittest.cc

Index: ash/wm/panels/panel_layout_manager_unittest.cc
diff --git a/ash/wm/panels/panel_layout_manager_unittest.cc b/ash/wm/panels/panel_layout_manager_unittest.cc
index 7c61f738f3248a70414a399a3021e0aa37cd91a7..e3871388a4d629682ec64de84c6fa2b79dc8dede 100644
--- a/ash/wm/panels/panel_layout_manager_unittest.cc
+++ b/ash/wm/panels/panel_layout_manager_unittest.cc
@@ -236,12 +236,12 @@ class PanelLayoutManagerTest : public test::AshTestBase {
     test_api.RunMessageLoopUntilAnimationsDone();
   }
 
-  void SetAlignment(aura::RootWindow* root_window, ShelfAlignment alignment) {
+  void SetAlignment(aura::Window* root_window, ShelfAlignment alignment) {
     ash::Shell* shell = ash::Shell::GetInstance();
     shell->SetShelfAlignment(alignment, root_window);
   }
 
-  ShelfAlignment GetAlignment(aura::RootWindow* root_window) {
+  ShelfAlignment GetAlignment(aura::Window* root_window) {
     ash::Shell* shell = ash::Shell::GetInstance();
     return shell->GetShelfAlignment(root_window);
   }