Splits debug_commands into aura and non-aura parts

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index ab8d6ed3dee5f557a1ddae50c7e91d51536d9e87..515f4f926275f8dbbf30d0a5792ca0c95a55f59c 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -52,6 +52,8 @@ class WindowManager : public ::ui::WindowManagerDelegate,
 
   WmShellMus* shell() { return shell_.get(); }
 
+  ::ui::WindowTreeClient* window_tree_client() { return window_tree_client_; }
+
   ::ui::WindowManagerClient* window_manager_client() {
     return window_manager_client_;
   }