Stop precomputing ClassElement.isValidMixin.

pkg/analyzer/test/src/summary/resynthesize_test.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.
 
 library test.src.serialization.elements_test;
 
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/type.dart';
@@ skipping 202 matching lines @@
     expect(resynthesized.name, original.name);
     expect(resynthesized.nameOffset, original.nameOffset, reason: desc);
     expect(resynthesized.documentationComment, original.documentationComment,
         reason: desc);
     expect(resynthesized.docRange, original.docRange, reason: desc);
     // Modifiers are a pain to test via handles.  So just test them via the
     // actual element.
     ElementImpl actualResynthesized = getActualElement(resynthesized, desc);
     ElementImpl actualOriginal = getActualElement(original, desc);
     for (Modifier modifier in Modifier.values) {
-      if (modifier == Modifier.MIXIN) {
-        // Skipping for now.  TODO(paulberry): fix.
-        continue;
-      }
       bool got = actualResynthesized.hasModifier(modifier);
       bool want = actualOriginal.hasModifier(modifier);
       expect(got, want,
           reason: 'Mismatch in $desc.$modifier: got $got, want $want');
     }
   }
 
   void compareExecutableElements(ExecutableElement resynthesized,
       ExecutableElement original, String desc) {
     compareElements(resynthesized, original, desc);
@@ skipping 1498 matching lines @@
       fail('Unexpectedly tried to get unlinked summary for $uri');
     }
     return serializedUnit;
   }
 
   @override
   bool hasLibrarySummary(String uri) {
     return true;
   }
 }