Fixed panel callout widgets showing up in the overview.

ash/wm/overview/window_grid.cc

Index: ash/wm/overview/window_grid.cc
diff --git a/ash/wm/overview/window_grid.cc b/ash/wm/overview/window_grid.cc
index e59d078bf3accc0c87fd28249a6d8fe57e7d872c..796684993bba32ef4fb5128bb57bcd0733eee291 100644
--- a/ash/wm/overview/window_grid.cc
+++ b/ash/wm/overview/window_grid.cc
@@ -143,7 +143,7 @@ WindowGrid::WindowGrid(aura::Window* root_window,
       // Attached panel windows are grouped into a single overview item per
       // grid.
       if (!panels_item) {
-        panels_item = new WindowSelectorPanels();
+        panels_item = new WindowSelectorPanels(root_window_);
         window_list_.push_back(panels_item);
       }
       panels_item->AddWindow(*iter);