Introduce ClassLike, MemberLike, FieldLike and FunctionLike

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

+// Copyright (c) 2016, 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.
+
+library entities;
+
+import 'elements.dart' show Entity;
+
+/// Stripped down super interface for class like entities.
+///
+/// Currently only [ClassElement] but later also kernel based Dart classes
+/// and/or Dart-in-JS classes.
+abstract class ClassEntity extends Entity {
+  bool get isClosure;
+  void forEachInstanceField(f(ClassEntity cls, FieldEntity field),
+      {bool includeSuperAndInjectedMembers: false});
+}
+
+/// Stripped down super interface for member like entities, that is,
+/// constructors, methods, fields etc.
+///
+/// Currently only [MemberElement] but later also kernel based Dart members
+/// and/or Dart-in-JS properties.
+abstract class MemberEntity extends Entity {
+  bool get isField;
+  bool get isFunction;
+  bool get isGetter;
+  bool get isAssignable;
+  ClassEntity get enclosingClass;
+}
+
+/// Stripped down super interface for field like entities.
+///
+/// Currently only [FieldElement] but later also kernel based Dart fields
+/// and/or Dart-in-JS field-like properties.
+abstract class FieldEntity extends MemberEntity {}
+
+/// Stripped down super interface for function like entities.
+///
+/// Currently only [FieldElement] but later also kernel based Dart constructors
+/// and methods and/or Dart-in-JS function-like properties.
+abstract class FunctionEntity extends MemberEntity {}