Add simple test migration helper.

tools/migration/lib/src/log.dart

+// 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:io';
+
+final _cyan = _getSpecial('\u001b[36m');
+final _green = _getSpecial('\u001b[32m');
+final _magenta = _getSpecial('\u001b[35m');
+final _red = _getSpecial('\u001b[31m');
+final _yellow = _getSpecial('\u001b[33m');
+final _blue = _getSpecial('\u001b[34m');
+final _gray = _getSpecial('\u001b[1;30m');
+final _none = _getSpecial('\u001b[0m');
+final _noColor = _getSpecial('\u001b[39m');
+final _bold = _getSpecial('\u001b[1m');
+
+void done(Object message) {
+  print("  ${green('(DONE)')} $message");
+}
+
+void note(Object message) {
+  print("  ${cyan('(NOTE)')} $message");
+}
+
+void todo(Object message) {
+  print("${red('(TODO)')} $message");
+}
+
+String bold(text) => "$_bold$text$_none";
+
+String cyan(text) => "$_cyan$text$_noColor";
+
+String green(text) => "$_green$text$_noColor";
+
+String red(text) => "$_red$text$_noColor";
+
+/// Gets a "special" string (ANSI escape or Unicode).
+///
+/// On Windows or when not printing to a terminal, returns something else since
+/// those aren't supported.
+String _getSpecial(String special, [String onWindows = '']) {
+  if (Platform.operatingSystem == 'windows' ||
+      stdioType(stdout) != StdioType.TERMINAL) {
+    return onWindows;
+  }
+
+  return special;
+}