Allows menu host windows to be enumerated in DragTargetWindowFinder

ui/views/widget/desktop_aura/x11_desktop_handler.cc

Index: ui/views/widget/desktop_aura/x11_desktop_handler.cc
diff --git a/ui/views/widget/desktop_aura/x11_desktop_handler.cc b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
index 3aa874da6234a674f7da598cd6b0605dea1b0910..46aef1728fe522ff4a2fc898b01ceb8687a0c88f 100644
--- a/ui/views/widget/desktop_aura/x11_desktop_handler.cc
+++ b/ui/views/widget/desktop_aura/x11_desktop_handler.cc
@@ -10,7 +10,9 @@
 #include "base/message_loop/message_loop.h"
 #include "ui/aura/env.h"
 #include "ui/aura/window_event_dispatcher.h"
+#include "ui/base/x/x11_menu_list.h"
 #include "ui/base/x/x11_util.h"
+#include "ui/gfx/x/x11_error_tracker.h"
 
 #if !defined(OS_CHROMEOS)
 #include "ui/views/ime/input_method.h"
@@ -138,6 +140,26 @@ uint32_t X11DesktopHandler::Dispatch(const base::NativeEvent& event) {
       }
       break;
     }
+    // Menus created by Chrome can be drag and drop targets. Since they are
+    // direct children of the screen root window and have override_redirect
+    // we cannot use regular _NET_CLIENT_LIST_STACKING property to find them
+    // and use a separate cache to keep track of them.
+    // TODO(varkha): Implement caching of all top level X windows and their
+    // coordinates and stacking order to eliminate repeated calls to X server
+    // during mouse movement, drag and shaping events.
+    case CreateNotify: {
+      // The window might be destroyed if the message pump haven't gotten a
+      // chance to run but we can safely ignore the X error.
+      gfx::X11ErrorTracker error_tracker;
+      XCreateWindowEvent *xcwe = &event->xcreatewindow;
+      ui::XMenuList::GetInstance()->MaybeRegisterMenu(xcwe->window);
+      break;
+    }
+    case DestroyNotify: {
+      XDestroyWindowEvent *xdwe = &event->xdestroywindow;
+      ui::XMenuList::GetInstance()->MaybeUnregisterMenu(xdwe->window);
+      break;
+    }
   }
 
   return POST_DISPATCH_NONE;