make menus, bubbles, etc. top level windows on aura

ui/aura/root_window_host.h

Index: ui/aura/root_window_host.h
diff --git a/ui/aura/root_window_host.h b/ui/aura/root_window_host.h
index 424968cd988843c1c8a5189d19038ee868d94553..3ae32baaa597054636bad8800001c4012be51ec4 100644
--- a/ui/aura/root_window_host.h
+++ b/ui/aura/root_window_host.h
@@ -122,6 +122,11 @@ class AURA_EXPORT RootWindowHost {
 
   // Stop listening events in preparation for shutdown.
   virtual void PrepareForShutdown() = 0;
+
+  // Notifies how much the host window will need to be expanded in order to
+  // contain layer animation in excess of the regular size. Layer bounds and
+  // the size of the root window are unaffected.
+  virtual void SetHostWindowExpansion(const gfx::Rect& extra) = 0;
 };
 
 }  // namespace aura