Add initial libfuzzers for fm2js transpiling and XML parsing.

testing/libfuzzer/pdf_fm2js_fuzzer.cc

+// Copyright 2016 The PDFium 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 <cstddef>
+#include <cstdint>
+
+#include "core/include/fxcrt/fx_basic.h"
+#include "core/include/fxcrt/fx_string.h"
+#include "xfa/src/fxfa/src/fm2js/xfa_fm2js.h"
+
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size) {
+  if (size > std::numeric_limits<FX_STRSIZE>::max())
+    return 0;
+
+  CFX_WideString input = CFX_WideString::FromUTF8(
+      reinterpret_cast<const char*>(data), static_cast<FX_STRSIZE>(size));
+  CXFA_FMProgram program;
+  if (program.Init(input) || program.ParseProgram())
+    return 0;
+
+  CFX_WideTextBuf js;
+  program.TranslateProgram(js);
+  return 0;
+}