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

ash/accelerators/exit_warning_handler.cc

Index: ash/accelerators/exit_warning_handler.cc
diff --git a/ash/accelerators/exit_warning_handler.cc b/ash/accelerators/exit_warning_handler.cc
index 6ea635ac052cdff8c9176cfdd0070e7e4106f0c7..1f8b53e45b263051a79e3a5c7e7031b711379e5f 100644
--- a/ash/accelerators/exit_warning_handler.cc
+++ b/ash/accelerators/exit_warning_handler.cc
@@ -11,7 +11,7 @@
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "grit/ash_strings.h"
-#include "ui/aura/root_window.h"
+#include "ui/aura/window.h"
 #include "ui/base/accessibility/accessible_view_state.h"
 #include "ui/base/l10n/l10n_util.h"
 #include "ui/base/resource/resource_bundle.h"
@@ -165,7 +165,7 @@ void ExitWarningHandler::CancelTimer() {
 void ExitWarningHandler::Show() {
   if (widget_)
     return;
-  aura::RootWindow* root_window = Shell::GetTargetRootWindow();
+  aura::Window* root_window = Shell::GetTargetRootWindow();
   ExitWarningWidgetDelegateView* delegate = new ExitWarningWidgetDelegateView;
   gfx::Size rs = root_window->bounds().size();
   gfx::Size ps = delegate->GetPreferredSize();