Fix csslib test failures on IE10.

pkg/csslib/test/mixin_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 mixin_test;
 
 import 'package:unittest/unittest.dart';
 import 'testing.dart';
 
 final options = ['--warnings_as_errors', '--no-colors', 'memory'];
@@ skipping 599 matching lines @@
   expect(error.span.end.offset, 69);
   error = errors[1];
   expect(error.message, 'expected :, but found }');
   expect(error.span.start.line, 7);
   expect(error.span.end.offset, 73);
   error = errors[2];
   expect(error.message, 'parsing error expected }');
   expect(error.span.start.line, 9);
   expect(error.span.end.offset, 83);
   error = errors[3];
-  expect(error.message, 'expected {, but found end of file(\n)');
+  expect(error.message, 'expected {, but found end of file()');
   expect(error.span.start.line, 9);
   expect(error.span.end.offset, 86);
   error = errors[4];
   expect(error.message, 'expected }, but found end of file()');
   expect(error.span.start.line, 10);
   expect(error.span.end.offset, 86);
   error = errors[5];
   expect(error.message, 'Using top-level mixin a as a declaration');
   expect(error.span.start.line, 5);
   expect(error.span.end.offset, 56);
@@ skipping 25 matching lines @@
     test('multiple args and var decls as args', mixinManyArgs);
   });
 
   group('Mixin warnings', () {
     test('undefined top-level', undefinedTopLevel);
     test('undefined declaration', undefinedDeclaration);
     test('detect bad top-level as declaration', badDeclarationInclude);
     test('detect bad declaration as top-level', badTopInclude);
   });
 }