Support for @mixin, @include and @extend

pkg/csslib/test/var_test.dart

 // Copyright (c) 2013, 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.
 
 library var_test;
 
 import 'package:unittest/unittest.dart';
-import 'package:csslib/parser.dart';
-import 'package:csslib/visitor.dart';
 import 'testing.dart';
 
 void simpleVar() {
   final errors = [];
   final input = ''':root {
   var-color-background: red;
   var-color-foreground: blue;
 
   var-a: var(b);
   var-b: var(c);
@@ skipping 631 matching lines @@
 main() {
   test('Simple var', simpleVar);
   test('Expressions var', expressionsVar);
   test('Default value in var()', defaultVar);
   test('CSS Parser only var', parserVar);
   test('Var syntax', testVar);
   test('Cycles var', cyclesVar);
   test('Less syntax', testLess);
   test('Polyfill', polyfill);
 }