Use ansi color in the dartanalyzer cli output.

pkg/analyzer_cli/test/super_mixin_test.dart

Index: pkg/analyzer_cli/test/super_mixin_test.dart
diff --git a/pkg/analyzer_cli/test/super_mixin_test.dart b/pkg/analyzer_cli/test/super_mixin_test.dart
index de1ad1af92355b7db2f46bff3d87fdb33248e952..d5cec87b380244dcaae64a3a4bcd8376975e1989 100644
--- a/pkg/analyzer_cli/test/super_mixin_test.dart
+++ b/pkg/analyzer_cli/test/super_mixin_test.dart
@@ -6,6 +6,7 @@ library analyzer_cli.test.super_mixin;
 
 import 'dart:io';
 
+import 'package:analyzer_cli/src/ansi.dart' as ansi;
 import 'package:analyzer_cli/src/driver.dart' show Driver, errorSink, outSink;
 import 'package:path/path.dart' as path;
 import 'package:test/test.dart';
@@ -23,17 +24,21 @@ void main() {
   group('--supermixins', () {
     StringSink savedOutSink, savedErrorSink;
     int savedExitCode;
+
     setUp(() {
+      ansi.runningTests = true;
       savedOutSink = outSink;
       savedErrorSink = errorSink;
       savedExitCode = exitCode;
       outSink = new StringBuffer();
       errorSink = new StringBuffer();
     });
+
     tearDown(() {
       outSink = savedOutSink;
       errorSink = savedErrorSink;
       exitCode = savedExitCode;
+      ansi.runningTests = false;
     });
 
     test('produces errors when option absent', () async {
@@ -45,11 +50,11 @@ void main() {
       expect(
           stdout,
           contains(
-              "[error] The class 'C' can't be used as a mixin because it extends a class other than Object"));
+              "error • The class 'C' can't be used as a mixin because it extends a class other than Object"));
       expect(
           stdout,
           contains(
-              "[error] The class 'C' can't be used as a mixin because it references 'super'"));
+              "error • The class 'C' can't be used as a mixin because it references 'super'"));
       expect(stdout, contains('2 errors found.'));
       expect(errorSink.toString(), '');
     });