Add a fuzzer for gn's parser.

BUG=
NOTRY=true

Review-Url: https://codereview.chromium.org/2275683002
Cr-Original-Commit-Position: refs/heads/master@{#414106}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: e47a47636163bd171399c6426e834837a52b75b7

tools/gn/BUILD.gn

diff --git a/tools/gn/BUILD.gn b/tools/gn/BUILD.gn
index e3a21ff..81678fa 100644
--- a/tools/gn/BUILD.gn
+++ b/tools/gn/BUILD.gn
@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 import("//testing/test.gni")
+import("//testing/libfuzzer/fuzzer_test.gni")
 
 defines = [ "GN_BUILD" ]
 
@@ -346,3 +347,12 @@
     "//testing/gtest",
   ]
 }
+
+fuzzer_test("gn_parser_fuzzer") {
+  sources = [
+    "parser_fuzzer.cc",
+  ]
+  deps = [
+    ":gn_lib",
+  ]
+}

tools/gn/parser_fuzzer.cc

diff --git a/tools/gn/parser_fuzzer.cc b/tools/gn/parser_fuzzer.cc
new file mode 100644
index 0000000..c7b4325
--- /dev/null
+++ b/tools/gn/parser_fuzzer.cc
@@ -0,0 +1,24 @@
+// Copyright 2016 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 <stdint.h>
+
+#include "tools/gn/input_file.h"
+#include "tools/gn/parser.h"
+#include "tools/gn/source_file.h"
+#include "tools/gn/tokenizer.h"
+
+extern "C" int LLVMFuzzerTestOneInput(const unsigned char* data, size_t size) {
+  SourceFile source;
+  InputFile input(source);
+  input.SetContents(std::string(reinterpret_cast<const char*>(data), size));
+
+  Err err;
+  std::vector<Token> tokens = Tokenizer::Tokenize(&input, &err);
+
+  if (!err.has_error())
+    Parser::Parse(tokens, &err);
+
+  return 0;
+}