Support mixin application equivalence in impact_test.

pkg/compiler/lib/src/kernel/world_builder.dart

 // Copyright (c) 2017, 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.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../common.dart';
 import '../common/backend_api.dart';
 import '../common/names.dart';
 import '../compile_time_constants.dart';
@@ skipping 788 matching lines @@
       throw new ArgumentError("No library found for $member");
     }
     return builder._getLibrary(library);
   }
 
   KLibrary getLibraryForFunction(KFunction function) =>
       _getLibrary(function, builder._methodMap);
 
   KLibrary getLibraryForField(KField field) =>
       _getLibrary(field, builder._fieldMap);
+
+  KClass getSuperclassForClass(KClass cls) {
+    KClassEnv env = builder._classEnvs[cls.classIndex];
+    ir.Supertype supertype = env.cls.supertype;
+    if (supertype == null) return null;
+    return builder.getClass(supertype.classNode);
+  }
+
+  InterfaceType getMixinTypeForClass(KClass cls) {
+    KClassEnv env = builder._classEnvs[cls.classIndex];
+    ir.Supertype mixedInType = env.cls.mixedInType;
+    if (mixedInType == null) return null;
+    return builder.createInterfaceType(
+        mixedInType.classNode, mixedInType.typeArguments);
+  }
 }