pkg/csslib: fixed analysis error, more cleanup

pkg/csslib/test/testing.dart

Index: pkg/csslib/test/testing.dart
diff --git a/pkg/csslib/test/testing.dart b/pkg/csslib/test/testing.dart
index 168a4e59b2c205c60ea555c4266477dea34842ee..002c45247aabf2d15cf68a2d92e115d1221c3c87 100644
--- a/pkg/csslib/test/testing.dart
+++ b/pkg/csslib/test/testing.dart
@@ -18,7 +18,8 @@ void useMockMessages() {
  * CSS will allow any property/value pairs regardless of validity; all of our
  * tests (by default) will ensure that the CSS is really valid.
  */
-StyleSheet parseCss(String cssInput, {List errors, List opts}) =>
+StyleSheet parseCss(String cssInput, {List<Message> errors,
+  List<String> opts}) =>
   parse(cssInput, errors: errors, options: opts == null ?
       ['--no-colors', '--checked', '--warnings_as_errors', 'memory'] : opts);
 
@@ -27,13 +28,14 @@ StyleSheet parseCss(String cssInput, {List errors, List opts}) =>
  * CSS will allow any property/value pairs regardless of validity; all of our
  * tests (by default) will ensure that the CSS is really valid.
  */
-StyleSheet compileCss(String cssInput, {List errors, List opts,
+StyleSheet compileCss(String cssInput, {List<Message> errors, List<String> opts,
     bool polyfill: false, List<StyleSheet> includes: null}) =>
   compile(cssInput, errors: errors, options: opts == null ?
       ['--no-colors', '--checked', '--warnings_as_errors', 'memory'] : opts,
       polyfill: polyfill, includes: includes);
 
-StyleSheet polyFillCompileCss(input, {List errors, List opts}) =>
+StyleSheet polyFillCompileCss(input, {List<Message> errors,
+  List<String> opts}) =>
     compileCss(input, errors: errors, polyfill: true, opts: opts);
 
 /** CSS emitter walks the style sheet tree and emits readable CSS. */