Fix all strong mode errors and warnings.

test/big_1_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 big_1_test;
 
+import 'package:csslib/src/messages.dart';
 import 'package:test/test.dart';
 import 'testing.dart';
 
 compilePolyfillAndValidate(String input, String generated) {
-  var errors = [];
+  var errors = <Message>[];
   var stylesheet = polyFillCompileCss(input, errors: errors, opts: options);
   expect(stylesheet != null, true);
   expect(errors.isEmpty, true, reason: errors.toString());
   expect(prettyPrint(stylesheet), generated);
 }
 
 void big_test() {
   var input = r'''
 /********************************************************************
  * Kennedy colors
@@ skipping 1135 matching lines @@
 .tooltip a, .tooltip div, .tooltip span {
   color: #fff;
 }''';
 
   compilePolyfillAndValidate(input, generated);
 }
 
 main() {
   test('big #1', big_test);
 }