Add a fuzzer for gn's parser.

tools/gn/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//testing/test.gni")
+import("//testing/libfuzzer/fuzzer_test.gni")
 
 defines = [ "GN_BUILD" ]
 
 static_library("gn_lib") {
   configs += [ "//build/config:precompiled_headers" ]
 
   sources = [
     "action_target_generator.cc",
     "action_target_generator.h",
     "action_values.cc",
@@ skipping 323 matching lines @@
     "format_test_data/",
   ]
 
   deps = [
     ":gn_lib",
     "//base/test:run_all_unittests",
     "//base/test:test_support",
     "//testing/gtest",
   ]
 }
+
+fuzzer_test("gn_parser_fuzzer") {
+  sources = [
+    "parser_fuzzer.cc",
+  ]
+  deps = [
+    ":gn_lib",
+  ]
+}