Use ansi color in the dartanalyzer cli output.

pkg/analyzer_cli/lib/src/ansi.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';
+
+/// Public for testing.
+bool runningTests = false;
+
+bool terminalSupportsAnsi() {
+  return !runningTests &&
+      !Platform.isWindows &&
+      stdioType(stdout) == StdioType.TERMINAL;
+}
+
+class AnsiLogger {
+  final bool useAnsi;
+
+  String get cyan => _code('\u001b[36m');
+  String get green => _code('\u001b[32m');
+  String get magenta => _code('\u001b[35m');
+  String get red => _code('\u001b[31m');
+  String get yellow => _code('\u001b[33m');
+  String get blue => _code('\u001b[34m');
+  String get gray => _code('\u001b[1;30m');
+  String get none => _code('\u001b[0m');
+  String get noColor => _code('\u001b[39m');
+  String get bold => _code('\u001b[1m');
+
+  AnsiLogger(this.useAnsi);
+
+  String get bullet => (runningTests || !Platform.isWindows) ? '•' : '-';
+
+  String _code(String ansiCode) => useAnsi ? ansiCode : '';
+}