cleanup and improve A/B fasta test harness

pkg/front_end/tool/fasta/standard_deviation.dart

Index: pkg/front_end/tool/fasta/standard_deviation.dart
diff --git a/pkg/front_end/tool/fasta/standard_deviation.dart b/pkg/front_end/tool/fasta/standard_deviation.dart
index aa6e7846666438496e64e13bd8f3d4d3c7a5ae00..b8ba224b69b3d6dfa3fac86d2d2bc5a88667d7fe 100644
--- a/pkg/front_end/tool/fasta/standard_deviation.dart
+++ b/pkg/front_end/tool/fasta/standard_deviation.dart
@@ -1,3 +1,7 @@
+// Copyright (c) 2017, 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.
+
 import 'dart:math';
 
 double average(List<double> elapsedTimes) {