Add a library suitable for libfuzzer with a small unit test runner shell

test/fuzzer/fuzzer.cc

+// Copyright 2016 the V8 project 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 <stddef.h>
+#include <stdint.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+extern "C" int LLVMFuzzerInitialize(int* argc, char*** argv);
+extern "C" int LLVMFuzzerTestOneInput(const uint8_t* data, size_t size);
+
+int main(int argc, char* argv[]) {
+  if (LLVMFuzzerInitialize(&argc, &argv)) {
+    fprintf(stderr, "Failed to initialize fuzzer target\n");
+    return 1;
+  }
+
+  if (argc < 2) {
+    fprintf(stderr, "USAGE: %s <input>\n", argv[0]);
+    return 1;
+  }
+
+  FILE* input = fopen(argv[1], "rb");
+
+  if (!input) {
+    fprintf(stderr, "Failed to open '%s'\n", argv[1]);
+    return 1;
+  }
+
+  fseek(input, 0, SEEK_END);
+  long size = ftell(input);
+  fseek(input, 0, SEEK_SET);
+
+  uint8_t* data = reinterpret_cast<uint8_t*>(malloc(size));
+  if (!data) {
+    fclose(input);
+    fprintf(stderr, "Failed to allocate %ld bytes\n", size);
+    return 1;
+  }
+
+  size_t bytes_read = fread(data, 1, size, input);
+  fclose(input);
+
+  if (bytes_read != size) {
+    free(data);
+    fprintf(stderr, "Failed to read %s\n", argv[1]);
+    return 1;
+  }
+
+  int result = LLVMFuzzerTestOneInput(data, size);
+
+  free(data);
+
+  return result;
+}