Avoid issuing incorrect errors when super mixins are enabled

pkg/analyzer/test/src/task/strong/strong_test_helper.dart

 // Copyright (c) 2015, 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.
 
 // TODO(jmesserly): this file needs to be refactored, it's a port from
 // package:dev_compiler's tests
 library analyzer.test.src.task.strong.strong_test_helper;
 
 import 'dart:async';
 
@@ skipping 255 matching lines @@
   /// errors/warnings/hints match the expected value.
   ///
   /// See [addFile] for more information about how to encode expectations in
   /// the file text.
   ///
   /// Returns the main resolved library. This can be used for further checks.
   Future<CompilationUnit> check(
       {bool declarationCasts: true,
       bool implicitCasts: true,
       bool implicitDynamic: true,
-      List<String> nonnullableTypes:
-          AnalysisOptionsImpl.NONNULLABLE_TYPES}) async {
+      List<String> nonnullableTypes: AnalysisOptionsImpl.NONNULLABLE_TYPES,
+      bool superMixins: false}) async {
     _checkCalled = true;
 
     File mainFile =
         _resourceProvider.getFile(_resourceProvider.convertPath('/main.dart'));
     expect(mainFile.exists, true, reason: '`/main.dart` is missing');
 
     AnalysisOptionsImpl analysisOptions = new AnalysisOptionsImpl();
     analysisOptions.strongMode = true;
     analysisOptions.strongModeHints = true;
     analysisOptions.declarationCasts = declarationCasts;
     analysisOptions.implicitCasts = implicitCasts;
     analysisOptions.implicitDynamic = implicitDynamic;
     analysisOptions.nonnullableTypes = nonnullableTypes;
+    analysisOptions.enableSuperMixins = superMixins;
 
     var mockSdk = new MockSdk(resourceProvider: _resourceProvider);
     mockSdk.context.analysisOptions = analysisOptions;
 
     SourceFactory sourceFactory;
     {
       var uriResolver = new _TestUriResolver(_resourceProvider);
       sourceFactory =
           new SourceFactory([new DartUriResolver(mockSdk), uriResolver]);
     }
@@ skipping 173 matching lines @@
   @override
   Source resolveAbsolute(Uri uri, [Uri actualUri]) {
     if (uri.scheme == 'package') {
       return (provider.getResource(
               provider.convertPath('/packages/' + uri.path)) as File)
           .createSource(uri);
     }
     return super.resolveAbsolute(uri, actualUri);
   }
 }