compositor: always redirect passive button grabs to clutter

All WM events (passive button grabs and passive keyboard grabs)
are handled through clutter now, so we must make sure we spoof
them even if they happen on frames (because that's where we
grab on)

src/compositor/compositor.c

@@ -976,6 +976,28 @@ grab_op_is_clicking (MetaGrabOp grab_op)
     }
 }
 
+static gboolean
+event_is_passive_button_grab (MetaDisplay   *display,
+                              XIDeviceEvent *device_event)
+{
+  /* see display.c for which events are passive button
+     grabs (meta_display_grab_window_buttons() and
+     meta_display_handle_events())
+     we need to filter them here because normally they
+     would be sent to gtk+ (they are on gtk+ frame xwindow),
+     but we want to redirect them to clutter
+  */
+
+  if (device_event->evtype != XI_ButtonPress)
+    return FALSE;
+
+  if ((device_event->mods.effective & display->window_grab_modifiers) !=
+      display->window_grab_modifiers)
+    return FALSE;
+
+  return device_event->detail < 4;
+}
+
 /* Clutter makes the assumption that there is only one X window
  * per stage, which is a valid assumption to make for a generic
  * application toolkit. As such, it will ignore any events sent
@@ -1006,7 +1028,8 @@ maybe_spoof_event_as_stage_event (MetaCompScreen *info,
           /* If this is a window frame, and we think GTK+ needs to handle the event,
              let GTK+ handle it without mangling */
           if (window && window->frame && device_event->event == window->frame->xwindow &&
-              (display->grab_op == META_GRAB_OP_NONE || grab_op_is_clicking (display->grab_op)))
+              (grab_op_is_clicking (display->grab_op) ||
+               (display->grab_op == META_GRAB_OP_NONE && !event_is_passive_button_grab (display, device_event))))
             break;
 
         case XI_KeyPress: