Encapsulate the index based maps for entities.

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

Index: pkg/compiler/lib/src/kernel/elements.dart
diff --git a/pkg/compiler/lib/src/kernel/elements.dart b/pkg/compiler/lib/src/kernel/elements.dart
deleted file mode 100644
index 5c334fe2a61c6603edbe76fe0b2df7ea3fee10b4..0000000000000000000000000000000000000000
--- a/pkg/compiler/lib/src/kernel/elements.dart
+++ /dev/null
@@ -1,39 +0,0 @@
-// 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 interfaces for modeling elements derived from Kernel IR.
-
-import '../elements/entities.dart';
-
-abstract class IndexedLibrary implements LibraryEntity {
-  /// Library index used for fast lookup in [KernelToElementMapBase].
-  int get libraryIndex;
-}
-
-abstract class IndexedClass implements ClassEntity {
-  /// Class index used for fast lookup in [KernelToElementMapBase].
-  int get classIndex;
-}
-
-abstract class IndexedMember implements MemberEntity {
-  /// Member index used for fast lookup in [KernelToElementMapBase].
-  int get memberIndex;
-}
-
-abstract class IndexedFunction implements IndexedMember, FunctionEntity {}
-
-abstract class IndexedConstructor
-    implements IndexedFunction, ConstructorEntity {}
-
-abstract class IndexedField implements IndexedMember, FieldEntity {}
-
-abstract class IndexedTypeVariable implements TypeVariableEntity {
-  /// Type variable index used for fast lookup in [KernelToElementMapBase].
-  int get typeVariableIndex;
-}
-
-abstract class IndexedTypedef implements TypedefEntity {
-  /// Typedef index used for fast lookup in [KernelToElementMapBase].
-  int get typedefIndex;
-}