Use Ash's ShelfWindowWatcher for app panel windows.

ash/common/wm_window.h

Index: ash/common/wm_window.h
diff --git a/ash/common/wm_window.h b/ash/common/wm_window.h
index 3871d2f01262bbedf8a3fff432a015187d2719a3..f81130c0a6bd6ac6ffbe53cd73b6de0524e65ad3 100644
--- a/ash/common/wm_window.h
+++ b/ash/common/wm_window.h
@@ -14,6 +14,7 @@
 #include "third_party/skia/include/core/SkColor.h"
 #include "ui/base/ui_base_types.h"
 #include "ui/compositor/layer_animation_element.h"
+#include "ui/gfx/image/image_skia.h"
 #include "ui/wm/core/window_animations.h"
 #include "ui/wm/public/window_types.h"
 
@@ -138,6 +139,9 @@ class ASH_EXPORT WmWindow {
   virtual int GetIntProperty(WmWindowProperty key) = 0;
   virtual void SetIntProperty(WmWindowProperty key, int value) = 0;
 
+  virtual gfx::ImageSkia GetWindowIcon() = 0;
+  virtual gfx::ImageSkia GetAppIcon() = 0;
+
   wm::WindowState* GetWindowState() {
     return const_cast<wm::WindowState*>(
         const_cast<const WmWindow*>(this)->GetWindowState());