Add script to run fasta as a benchmark

pkg/front_end/tool/fasta_perf_test.dart

+// Copyright (c) 2016, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+/// The only purpose of this file is to enable analyzer tests on `perf.dart`,
+/// the code here just has a dummy import to the rest of the code.
+library front_end.tool.perf_test;
+
+import 'dart:io' show Platform;
+import 'fasta_perf.dart' as m;
+
+main() async {
+  var benchIds = [
+    'scan',
+    'kernel_gen_e2e',
+  ];
+  var inputFile = Platform.script.resolve('../lib/file_system.dart').path;
+  for (var id in benchIds) {
+    await m.main([id, inputFile]);
+  }
+}