Support for modular mixin resolution.

pkg/kernel/lib/transformations/mixin_full_resolution.dart

 // Copyright (c) 2016, 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 kernel.transformations.mixin_full_resolution;
 
 import '../ast.dart';
 import '../class_hierarchy.dart';
 import '../clone.dart';
 import '../core_types.dart';
 import '../type_algebra.dart';
@@ skipping 60 matching lines @@
     }
   }
 
   transformClass(Set<Class> processedClasses, Set<Class> transformedClasses,
       Class class_) {
     // If this class was already handled then so were all classes up to the
     // [Object] class.
     if (!processedClasses.add(class_)) return;
 
     // Ensure super classes have been transformed before this class.
-    if (class_.superclass != null) {
+    if (class_.superclass != null &&
+        class_.superclass.level.index >= ClassLevel.Mixin.index) {
       transformClass(processedClasses, transformedClasses, class_.superclass);
     }
 
     // If this is not a mixin application we don't need to make forwarding
     // constructors in this class.
     if (!class_.isMixinApplication) return;
 
-    if (class_.mixedInClass.level != ClassLevel.Body) {
+    if (class_.mixedInClass.level.index < ClassLevel.Mixin.index) {
       throw new Exception(
           'Class "${class_.name}" mixes in "${class_.mixedInClass.name}" from'
           ' an external library.  Did you forget --link?');
     }
 
     transformedClasses.add(class_);
 
     // Clone fields and methods from the mixin class.
     var substitution = getSubstitutionMap(class_.mixedInType);
     var cloner = new CloneVisitor(typeSubstitution: substitution);
@@ skipping 270 matching lines @@
           return null;
         }
       }
 
       throw new Exception(
           'Could not find a generative constructor named "${constructor.name}" '
           'in lookup class "${lookupClass.name}"!');
     }
   }
 }