Fleshes out the basic set of focus rules a bit more.

ui/views/corewm/window_modality_controller.cc

Index: ui/views/corewm/window_modality_controller.cc
===================================================================
--- ui/views/corewm/window_modality_controller.cc	(revision 170971)
+++ ui/views/corewm/window_modality_controller.cc	(working copy)
@@ -75,6 +75,11 @@
   child->SetProperty(kModalParentKey, parent);
 }
 
+aura::Window* GetModalTransientForActivatableWindow(
+    aura::Window* activatable) {
+  return GetModalTransientChild(activatable, activatable);
+}
+
 aura::Window* GetModalTransient(aura::Window* window) {
   if (!window)
     return NULL;