Use Entity in native_data.

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 547 matching lines @@
     MemberEntity member =
         worldBuilder.lookupClassMember(cls, name, setter: setter);
     if (member == null && required) {
       throw new SpannableAssertionFailure(CURRENT_ELEMENT_SPANNABLE,
           "The member '$name' was not found in ${cls.name}.");
     }
     return member;
   }
 
   @override
+  ClassEntity getSuperClass(ClassEntity cls) {
+    throw new UnimplementedError('KernelElementEnvironment.getSuperClass');
+  }
+
+  @override
   void forEachMixin(ClassEntity cls, void f(ClassEntity mixin)) {
     throw new UnimplementedError('KernelElementEnvironment.forEachMixin');
   }
 
   @override
   void forEachClassMember(
       ClassEntity cls, void f(ClassEntity declarer, MemberEntity member)) {
     throw new UnimplementedError(
         'KernelElementEnvironment.forEachInstanceMember');
   }
@@ skipping 287 matching lines @@
   }
 
   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);
   }
 }