Change overview mode to so that docked panel windows are not grouped together.

ash/wm/overview/transparent_activate_window_button.cc

Index: ash/wm/overview/transparent_activate_window_button.cc
diff --git a/ash/wm/overview/transparent_activate_window_button.cc b/ash/wm/overview/transparent_activate_window_button.cc
index 212b57cc1bb2e1d6adbfead1d8f68e3beb2eb5e6..4189bf1e89e526bfcf0818393f18ebf5f83c212f 100644
--- a/ash/wm/overview/transparent_activate_window_button.cc
+++ b/ash/wm/overview/transparent_activate_window_button.cc
@@ -133,12 +133,4 @@ void TransparentActivateWindowButton::SendFocusAlert() const {
       NotifyAccessibilityEvent(ui::AX_EVENT_FOCUS, true);
 }
 
-void TransparentActivateWindowButton::StackAbove(
-    TransparentActivateWindowButton* activate_button) {
-  aura::Window* this_window = event_handler_widget_->GetNativeWindow();
-  aura::Window* other_window = activate_button->event_handler_widget_->
-      GetNativeWindow();
-  this_window->parent()->StackChildAbove(this_window, other_window);
-}
-
 }  // namespace ash