Allows menu host windows to be enumerated in DragTargetWindowFinder

ui/base/x/x11_util.h

 // Copyright (c) 2012 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_UTIL_H_
 #define UI_BASE_X_X11_UTIL_H_
 
 // This file declares utility functions for X11 (Linux only).
 //
 // These functions do not require the Xlib headers to be included (which is why
@@ skipping 11 matching lines @@
 #include "ui/events/keycodes/keyboard_codes.h"
 #include "ui/gfx/point.h"
 #include "ui/gfx/x/x11_types.h"
 
 typedef unsigned long Atom;
 typedef unsigned long XSharedMemoryId;  // ShmSeg in the X headers.
 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;
 typedef struct _GtkWindow GtkWindow;
 #endif
 
 namespace gfx {
 class Canvas;
 class Point;
 class Rect;
@@ skipping 349 matching lines @@
   ::Cursor get() const;
   void reset(::Cursor cursor);
 
  private:
   ::Cursor cursor_;
   XDisplay* display_;
 
   DISALLOW_COPY_AND_ASSIGN(XScopedCursor);
 };
 
+// Keeps track of created and destroyed top level menu windows.

[sadrul, 2014/03/22 17:55:18]

I was more hoping we would create a list of all top-level windows, and update it
from the Create/Destroy events from X. That would both fix this issue, and fix
the lag issue during dragging by not having to get the list of windows from X
for each mouse-move event.

+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_