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

ui/base/x/x11_util_internal.h

 // Copyright (c) 2011 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_INTERNAL_H_
 #define UI_BASE_X_X11_UTIL_INTERNAL_H_
 #pragma once
 
 // This file declares utility functions for X11 (Linux only).
 //
@@ skipping 32 matching lines @@
 UI_EXPORT void SetX11ErrorHandlers(XErrorHandler error_handler,
                                    XIOErrorHandler io_error_handler);
 
 // NOTE: This function should not be called directly from the
 // X11 Error handler because it queries the server to decode the
 // error message, which may trigger other errors. A suitable workaround
 // is to post a task in the error handler to call this function.
 UI_EXPORT void LogErrorEventDescription(Display* dpy,
                                         const XErrorEvent& error_event);
 
+// LOG(FATAL) if an X11 errors has been reported. Uses XSync to ensure that all
+// requests have been received and processed by the X server and uses the X
+// display contained in the reported XErrorEvent.
+UI_EXPORT void CheckForReportedX11Error();
+
 }  // namespace ui
 
 #endif  // UI_BASE_X_X11_UTIL_INTERNAL_H_