Apply a patch from Mozilla to prevent an integer overflow in expat.

third_party/expat/files/lib/xmlparse.c.original

 /* Copyright (c) 1998, 1999, 2000 Thai Open Source Software Center Ltd
    See the file COPYING for copying permission.
 */
 
 #include <stddef.h>
 #include <string.h>                     /* memset(), memcpy() */
 #include <assert.h>
 #include <limits.h>                     /* UINT_MAX */
 #include <time.h>                       /* time() */
 
@@ skipping 6383 matching lines @@
     return NULL;
   if (ret->name != name)
     poolDiscard(&dtd->pool);
   else {
     poolFinish(&dtd->pool);
     if (!setElementTypePrefix(parser, ret))
       return NULL;
   }
   return ret;
 }