Allows menu host windows to be enumerated in DragTargetWindowFinder

ui/base/x/x11_util.h

Index: ui/base/x/x11_util.h
diff --git a/ui/base/x/x11_util.h b/ui/base/x/x11_util.h
index dbcd987b9dd2984ac7b746302477c332c1602aeb..f38df6b0f790d70e1b3b7e857447d87783ea87ac 100644
--- a/ui/base/x/x11_util.h
+++ b/ui/base/x/x11_util.h
@@ -29,6 +29,9 @@ typedef unsigned long Cursor;
 typedef struct _XcursorImage XcursorImage;
 typedef union _XEvent XEvent;
 
+// A process wide singleton cache for X menus.
+template <typename T> struct DefaultSingletonTraits;
+
 #if defined(TOOLKIT_GTK)
 typedef struct _GdkDrawable GdkWindow;
 typedef struct _GtkWidget GtkWidget;
@@ -398,6 +401,31 @@ class UI_BASE_EXPORT XScopedCursor {
   DISALLOW_COPY_AND_ASSIGN(XScopedCursor);
 };
 
+// Keeps track of created and destroyed top level menu windows.
+class UI_BASE_EXPORT XMenuList {
+ public:
+  static XMenuList* GetInstance();
+
+  // Checks if |menu| has _NET_WM_WINDOW_TYPE property set to
+  // "_NET_WM_WINDOW_TYPE_MENU" atom and if so caches it.
+  void MaybeRegisterMenu(XID menu);
+
+  // Finds |menu| in cache and if found removes it.
+  void MaybeUnregisterMenu(XID menu);
+
+  // Inserts cached menu XIDs at the beginning of |stack|.
+  void InsertMenuWindowXIDs(std::vector<XID>* stack);
+
+ private:
+  friend struct DefaultSingletonTraits<XMenuList>;
+  XMenuList();
+  ~XMenuList();
+
+  std::vector<XID> menus_;
+  ::Atom menu_type_atom_;
+  DISALLOW_COPY_AND_ASSIGN(XMenuList);
+};
+
 }  // namespace ui
 
 #endif  // UI_BASE_X_X11_UTIL_H_