Check equivalence on impact computed with KernelWorldBuilder.

pkg/compiler/lib/src/kernel/elements.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.
 
 /// Entity model for elements derived from Kernel IR.
 
 import '../elements/elements.dart';
 import '../elements/entities.dart';
 
 class KLibrary implements LibraryEntity {
   /// Library index used for fast lookup in [KernelWorldBuilder].
   final int libraryIndex;
   final String name;
   final String libraryName;
 
   KLibrary(this.libraryIndex, this.name, this.libraryName);
 
   String toString() => 'library($name)';
 }
 
 class KClass implements ClassEntity {
+  /// Class index used for fast lookup in [KernelWorldBuilder].
+  final int classIndex;
   final String name;
 
-  KClass(this.name);
+  KClass(this.classIndex, this.name);
 
   @override
   bool get isClosure => false;
 
   String toString() => 'class($name)';
 }
 
 abstract class KMember implements MemberEntity {
   final KClass enclosingClass;
   final Name _name;
@@ skipping 126 matching lines @@
 
   String get _kind => 'field';
 }
 
 class KTypeVariable implements TypeVariableEntity {
   final Entity typeDeclaration;
   final String name;
   final int index;
 
   KTypeVariable(this.typeDeclaration, this.name, this.index);
+
+  String toString() => 'type_variable(${typeDeclaration.name}.$name)';
 }
 
 class KLocalFunction implements Local {
   final String name;
   final MemberEntity memberContext;
   final Entity executableContext;
 
   KLocalFunction(this.name, this.memberContext, this.executableContext);
+
+  String toString() =>
+      'local_function(${memberContext.name}.${name ?? '<anonymous>'})';
 }