Use Ash's ShelfWindowWatcher for app panel windows.

ash/common/shelf/shelf_item_delegate.h

Index: ash/common/shelf/shelf_item_delegate.h
diff --git a/ash/common/shelf/shelf_item_delegate.h b/ash/common/shelf/shelf_item_delegate.h
index 3452b83a5225bebe713528a691a1c13a4740348c..1358521ea3bb2cfc73f9504d5608d889dcaaf5ba 100644
--- a/ash/common/shelf/shelf_item_delegate.h
+++ b/ash/common/shelf/shelf_item_delegate.h
@@ -70,6 +70,9 @@ class ASH_EXPORT ShelfItemDelegate {
   // Returns true if a tooltip should be shown.
   virtual bool ShouldShowTooltip() = 0;
 
+  // Returns true if this item is open.
+  virtual bool IsOpen() const = 0;
+
   // Closes all windows associated with this item.
   virtual void Close() = 0;
 };