ash: Fix event processing in modal windows in login/lock screen.

ash/wm/system_modal_container_layout_manager_unittest.cc

Index: ash/wm/system_modal_container_layout_manager_unittest.cc
diff --git a/ash/wm/system_modal_container_layout_manager_unittest.cc b/ash/wm/system_modal_container_layout_manager_unittest.cc
index 90a6a19258252cf45443543322fe7df00f7ef7a2..bea55eeca05cac9c2316ff8b990450ec5580bc84 100644
--- a/ash/wm/system_modal_container_layout_manager_unittest.cc
+++ b/ash/wm/system_modal_container_layout_manager_unittest.cc
@@ -39,7 +39,7 @@ bool AllRootWindowsHaveModalBackgrounds() {
            controllers.begin();
        iter != controllers.end(); ++iter) {
     has_modal_screen &=
-        (*iter)->GetSystemModalLayoutManager()->has_modal_background();
+        (*iter)->GetSystemModalLayoutManager(NULL)->has_modal_background();
   }
   return has_modal_screen;
 }