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).
 //
 // These functions require the inclusion of the Xlib headers. Since the Xlib
 // headers pollute so much of the namespace, this should only be included
 // when needed.
 
 extern "C" {
 #include <X11/Xatom.h>
+#include <X11/Xdefs.h>
 #include <X11/Xlib.h>
 #include <X11/extensions/XShm.h>
 #include <X11/extensions/Xrender.h>
 }
 
 #include "ui/base/ui_export.h"
 
 namespace ui {
 
 // --------------------------------------------------------------------------
@@ skipping 16 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);
 
+// Returns the last X11 error encountered and clears it. Calls XSync to ensure
+// all requests have been received and processed by the X server.

[Ami GONE FROM CHROMIUM, 2011/09/14 23:23:11]

Document semantics of NULL return.

[Ami GONE FROM CHROMIUM, 2011/09/14 23:23:11]

If you really returned a pointer here you'd want you to doco the ownership
semantics of it (but see .cc commentary).

+UI_EXPORT XErrorEvent* GetLastX11Error(Display* display);

[Ami GONE FROM CHROMIUM, 2011/09/14 23:23:11]

s/Get/GetAndClear/

[Ami GONE FROM CHROMIUM, 2011/09/14 23:23:11]

I wonder about the threading semantics here.  Do you not need to restrict
callers to the thread dealing w/ xlib?
(xlib is thread-unsafe)

+
 }  // namespace ui
 
 #endif  // UI_BASE_X_X11_UTIL_INTERNAL_H_