Disallow mixing in classes that use 'super'.

sdk/lib/_internal/compiler/implementation/elements/elements.dart

 // Copyright (c) 2012, 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 elements;
 
 import 'dart:uri';
 
 import 'modelx.dart';
 import '../tree/tree.dart';
@@ skipping 181 matching lines @@
 
   bool hasFixedBackendName();
   String fixedBackendName();
 
   bool isAbstract(Compiler compiler);
   bool isForeign(Compiler compiler);
 
   void addMetadata(MetadataAnnotation annotation);
   void setNative(String name);
   void setFixedBackendName(String name);
+
   Scope buildScope();
 }
 
 class Elements {
   static bool isUnresolved(Element e) {
     return e == null || e.isErroneous();
   }
   static bool isErroneousElement(Element e) => e != null && e.isErroneous();
 
   static bool isClass(Element e) => e != null && e.kind == ElementKind.CLASS;
@@ skipping 549 matching lines @@
   Element get annotatedElement;
   int get resolutionState;
   Token get beginToken;
 
   // TODO(kasperl): Try to get rid of these.
   void set annotatedElement(Element value);
   void set resolutionState(int value);
 
   MetadataAnnotation ensureResolved(Compiler compiler);
 }