port libxml_xml_read_memory_fuzzer (from kcc's libfuzzer-bot) and disable error messages from the p…

testing/libfuzzer/fuzzers/libxml_xml_read_memory_fuzzer.cc

+// Copyright (c) 2015 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.
+
+#include "libxml/parser.h"
+
+void ignore (void * ctx, const char * msg, ...) {
+  // Error handler to avoid spam of error messages from libxml parser.
+}
+
+extern "C" int LLVMFuzzerTestOneInput(const unsigned char *data, size_t size) {
+  xmlSetGenericErrorFunc(NULL, &ignore);
+
+  if (auto doc = xmlReadMemory(reinterpret_cast<const char *>(data),
+                               size, "noname.xml", NULL, 0)) {
+    xmlFreeDoc(doc);
+  }
+
+  return 0;
+}