Use Ash's ShelfWindowWatcher for app panel windows.

ash/common/shelf/shelf_controller.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/common/shelf/shelf_controller.h"
 
 #include "ash/common/shelf/shelf_item_delegate.h"
 #include "ash/common/shelf/shelf_menu_model.h"
 #include "ash/common/shelf/wm_shelf.h"
 #include "ash/common/wm_lookup.h"
@@ skipping 103 matching lines @@
     return new ShelfMenuModelMus(this);
   }
 
   bool IsDraggable() override {
     NOTIMPLEMENTED();
     return false;
   }
 
   bool ShouldShowTooltip() override { return true; }
 
+  bool IsOpen() const override { return true; }
+
   void Close() override { NOTIMPLEMENTED(); }
 
   mojom::ShelfItemDelegateAssociatedPtr delegate_;
   bool pinned_ = false;
   std::map<uint32_t, base::string16> window_id_to_title_;
   base::string16 title_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfItemDelegateMus);
 };
 
@@ skipping 141 matching lines @@
     return;
   ShelfID shelf_id = app_id_to_shelf_id_[app_id];
   int index = model_.ItemIndexByID(shelf_id);
   DCHECK_GE(index, 0);
   ShelfItem item = *model_.ItemByID(shelf_id);
   item.image = GetShelfIconFromBitmap(image);
   model_.Set(index, item);
 }
 
 }  // namespace ash