Encapsulate the index based maps for entities.

tests/compiler/dart2js/kernel/test_helpers.dart

Index: tests/compiler/dart2js/kernel/test_helpers.dart
diff --git a/tests/compiler/dart2js/kernel/test_helpers.dart b/tests/compiler/dart2js/kernel/test_helpers.dart
index 5aaa6619df7e9e324d12d9a3fa4d6c091addf45d..4a9bf9dbbd637a22521f05385f7e5e0082571a97 100644
--- a/tests/compiler/dart2js/kernel/test_helpers.dart
+++ b/tests/compiler/dart2js/kernel/test_helpers.dart
@@ -15,10 +15,10 @@ import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/elements/resolution_types.dart';
 import 'package:compiler/src/elements/types.dart';
 import 'package:compiler/src/enqueue.dart';
-import 'package:compiler/src/kernel/elements.dart';
-import 'package:compiler/src/kernel/kelements.dart' show KLocalFunction;
 import 'package:compiler/src/kernel/element_map.dart';
 import 'package:compiler/src/kernel/element_map_impl.dart';
+import 'package:compiler/src/kernel/indexed.dart';
+import 'package:compiler/src/kernel/kelements.dart' show KLocalFunction;
 import 'package:compiler/src/serialization/equivalence.dart';
 import 'package:compiler/src/ssa/kernel_impact.dart';
 import 'package:compiler/src/universe/world_impact.dart';