Use Ash's ShelfWindowWatcher for app panel windows.

ash/common/shelf/shelf_window_watcher.h

Index: ash/common/shelf/shelf_window_watcher.h
diff --git a/ash/common/shelf/shelf_window_watcher.h b/ash/common/shelf/shelf_window_watcher.h
index 45565e8f4b67f375d0109445f62bf5a321277683..9eb3cd2aed1d61bbcd389da46ddc128d6f3571b1 100644
--- a/ash/common/shelf/shelf_window_watcher.h
+++ b/ash/common/shelf/shelf_window_watcher.h
@@ -5,6 +5,8 @@
 #ifndef ASH_COMMON_SHELF_SHELF_WINDOW_WATCHER_H_
 #define ASH_COMMON_SHELF_SHELF_WINDOW_WATCHER_H_
 
+#include <set>
+
 #include "ash/common/wm_activation_observer.h"
 #include "ash/common/wm_window_observer.h"
 #include "base/macros.h"
@@ -17,10 +19,11 @@ class ShelfModel;
 class WmWindow;
 
 // ShelfWindowWatcher creates and handles a ShelfItem for windows in the default
-// container that have a valid ShelfItemType property (e.g. the task manager
-// dialog or the OS settings window). It adds the ShelfItem when the window is
-// added to the default container and maintains it until the window is closed,
-// even if the window is transiently reparented (e.g. during a drag).
+// container and panels in the panel container that have a valid ShelfItemType
+// property (e.g. the task manager dialog or the OS settings window). It adds
+// the ShelfItem when the window is added to the default container and maintains
+// it until the window is closed, even if the window is transiently reparented
+// (e.g. during a drag).
 class ShelfWindowWatcher : public WmActivationObserver,
                            public display::DisplayObserver {
  public:
@@ -69,10 +72,7 @@ class ShelfWindowWatcher : public WmActivationObserver,
   // Removes a ShelfItem for |window|.
   void RemoveShelfItem(WmWindow* window);
 
-  // Updates the status of ShelfItem for |window|.
-  void UpdateShelfItemStatus(WmWindow* window, bool is_active);
-
-  // Returns the index of ShelfItem associated with |window|.
+  // Returns the index of ShelfItem associated with |window|, or -1 if none.
   int GetShelfItemIndexForWindow(WmWindow* window) const;
 
   // Cleans up observers on |container|.
@@ -106,6 +106,9 @@ class ShelfWindowWatcher : public WmActivationObserver,
   ScopedObserver<WmWindow, ContainerWindowObserver> observed_container_windows_;
   ScopedObserver<WmWindow, UserWindowObserver> observed_user_windows_;
 
+  // The set of windows with shelf items managed by this ShelfWindowWatcher.
+  std::set<WmWindow*> user_windows_with_items_;
+
   DISALLOW_COPY_AND_ASSIGN(ShelfWindowWatcher);
 };