Change X11 error handler override to allow easy X11 error checking.

ui/base/x/x11_util_internal.h

Index: ui/base/x/x11_util_internal.h
diff --git a/ui/base/x/x11_util_internal.h b/ui/base/x/x11_util_internal.h
index 70eb088c786e8668e48eb2f65f14f0d0a425a423..b481d90758d195b17b7972a6da82c29c7f6f7773 100644
--- a/ui/base/x/x11_util_internal.h
+++ b/ui/base/x/x11_util_internal.h
@@ -50,6 +50,11 @@ UI_EXPORT void SetX11ErrorHandlers(XErrorHandler error_handler,
 UI_EXPORT void LogErrorEventDescription(Display* dpy,
                                         const XErrorEvent& error_event);
 
+// CHECK that no X11 errors have been reported. Uses XSync to ensure that all
+// requests have been received and processed by the X server. Uses the default X
+// display.
+UI_EXPORT void CheckFailOnReportedX11Error();
+
 }  // namespace ui
 
 #endif  // UI_BASE_X_X11_UTIL_INTERNAL_H_