Use Ash's ShelfWindowWatcher for app panel windows.

ash/mus/bridge/wm_window_mus.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/mus/bridge/wm_window_mus.h"
 
 #include "ash/common/shelf/shelf_item_types.h"
 #include "ash/common/wm/container_finder.h"
 #include "ash/common/wm/window_positioning_utils.h"
 #include "ash/common/wm/window_state.h"
@@ skipping 473 matching lines @@
 
   if (key == WmWindowProperty::TOP_VIEW_INSET) {
     // TODO: need support for TOP_VIEW_INSET: http://crbug.com/615100.
     NOTIMPLEMENTED();
     return;
   }
 
   NOTREACHED();
 }
 
+gfx::ImageSkia WmWindowMus::GetWindowIcon() {
+  NOTIMPLEMENTED();
+  return gfx::ImageSkia();
+}
+
+gfx::ImageSkia WmWindowMus::GetAppIcon() {
+  NOTIMPLEMENTED();
+  return gfx::ImageSkia();
+}
+
 const wm::WindowState* WmWindowMus::GetWindowState() const {
   return window_state_.get();
 }
 
 WmWindow* WmWindowMus::GetToplevelWindow() {
   return WmShellMus::GetToplevelAncestor(window_);
 }
 
 WmWindow* WmWindowMus::GetToplevelWindowForFocus() {
   // TODO(sky): resolve if we really need two notions of top-level. In the mus
@@ skipping 520 matching lines @@
 }
 
 void WmWindowMus::OnTransientChildRemoved(ui::Window* window,
                                           ui::Window* transient) {
   for (auto& observer : transient_observers_)
     observer.OnTransientChildRemoved(this, Get(transient));
 }
 
 }  // namespace mus
 }  // namespace ash