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

ui/base/x/x11_util.cc

Index: ui/base/x/x11_util.cc
diff --git a/ui/base/x/x11_util.cc b/ui/base/x/x11_util.cc
index 82cdab78f54bc87e603501517f112e3db282c54e..374ceaf77681456a0db51bdac7215742c38190ec 100644
--- a/ui/base/x/x11_util.cc
+++ b/ui/base/x/x11_util.cc
@@ -68,6 +68,14 @@ int DefaultX11IOErrorHandler(Display* d) {
   _exit(1);
 }
 
+XErrorHandler current_error_handler = DefaultX11ErrorHandler;
+XErrorEvent* last_error_event = NULL;
+
+int BaseX11ErrorHandler(Display* d, XErrorEvent* e) {
+  last_error_event = e;

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

(this is the comment referenced from the .h comment)
Is there any reason to believe |e| will continue to point to valid data after
this returns?
I imagined there'd be a memcpy here into an error struct that this file owned,
and that the getter would further memcpy a copy for each caller.

+  return current_error_handler(d, e);
+}
+
 // Note: The caller should free the resulting value data.
 bool GetProperty(XID window, const std::string& property_name, long max_length,
                  Atom* type, int* format, unsigned long* num_items,
@@ -679,6 +687,7 @@ bool ChangeWindowDesktop(XID window, XID destination) {
 }
 
 void SetDefaultX11ErrorHandlers() {
+  XSetErrorHandler(BaseX11ErrorHandler);
   SetX11ErrorHandlers(NULL, NULL);
 }
 
@@ -710,6 +719,13 @@ bool IsX11WindowFullScreen(XID window) {
          monitor_rect.height == window_rect.height();
 }
 
+XErrorEvent* GetLastX11Error(Display* display) {
+  XSync(display, False);
+  XErrorEvent* e = last_error_event;
+  last_error_event = NULL;
+  return e;
+}
+
 // ----------------------------------------------------------------------------
 // These functions are declared in x11_util_internal.h because they require
 // XLib.h to be included, and it conflicts with many other headers.
@@ -788,9 +804,10 @@ XRenderPictFormat* GetRenderVisualFormat(Display* dpy, Visual* visual) {
 
 void SetX11ErrorHandlers(XErrorHandler error_handler,
                          XIOErrorHandler io_error_handler) {
-  XSetErrorHandler(error_handler ? error_handler : DefaultX11ErrorHandler);
-  XSetIOErrorHandler(
-      io_error_handler ? io_error_handler : DefaultX11IOErrorHandler);
+  current_error_handler = error_handler ?
+      error_handler : DefaultX11ErrorHandler;
+  XSetIOErrorHandler(io_error_handler ?
+                     io_error_handler : DefaultX11IOErrorHandler);
 }
 
 void LogErrorEventDescription(Display* dpy,