Allows menu host windows to be enumerated in DragTargetWindowFinder

ui/base/x/x11_menu_list.h

Index: ui/base/x/x11_menu_list.h
diff --git a/ui/base/x/x11_menu_list.h b/ui/base/x/x11_menu_list.h
new file mode 100644
index 0000000000000000000000000000000000000000..4e8476aea088b75cf387925d2f459e70522e7586
--- /dev/null
+++ b/ui/base/x/x11_menu_list.h
@@ -0,0 +1,48 @@
+// Copyright (c) 2014 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.
+
+#ifndef UI_BASE_X_X11_MENU_LIST_H_
+#define UI_BASE_X_X11_MENU_LIST_H_
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "ui/base/ui_base_export.h"
+#include "ui/gfx/x/x11_types.h"
+
+typedef unsigned long Atom;
+
+// A process wide singleton cache for X menus.
+template <typename T> struct DefaultSingletonTraits;
+
+namespace ui {
+
+// 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_MENU_LIST_H_