Converts remaining usage of WmLayoutManager to aura::LayoutManager

ash/root_window_controller.h

Index: ash/root_window_controller.h
diff --git a/ash/root_window_controller.h b/ash/root_window_controller.h
index 641710e8e32c39f4ed57107a549e895ac09af606..6f0945fd821330bad199472a4581507d4bd73ec5 100644
--- a/ash/root_window_controller.h
+++ b/ash/root_window_controller.h
@@ -179,7 +179,7 @@ class ASH_EXPORT RootWindowController : public ShellObserver {
   // modal container is used if the screen is currently locked. Otherwise, the
   // default modal container is used.
   SystemModalContainerLayoutManager* GetSystemModalLayoutManager(
-      WmWindow* window);
+      aura::Window* window);
 
   AlwaysOnTopController* always_on_top_controller() {
     return always_on_top_controller_.get();