Introduce TypedefEntity

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 'package:front_end/src/fasta/parser/async_modifier.dart'
     show AsyncModifier;
 
 import '../common.dart';
@@ skipping 33 matching lines @@
   LibraryEntity get library;
 
   /// Whether this is a synthesized class for a closurized method or local
   /// function.
   bool get isClosure;
 
   /// Whether this is an abstract class.
   bool get isAbstract;
 }
 
+abstract class TypedefEntity extends Entity {
+  LibraryEntity get library;
+}
+
 abstract class TypeVariableEntity extends Entity {
   /// The class or generic method that declared this type variable.
   Entity get typeDeclaration;
 
   /// The index of this type variable in the type variables of its
   /// [typeDeclaration].
   int get index;
 }
 
 /// Stripped down super interface for member like entities, that is,
@@ skipping 202 matching lines @@
   /// The total number of parameters (required or optional).
   int get totalParameters => positionalParameters + namedParameters.length;
 
   /// Returns the [CallStructure] corresponding to a call site passing all
   /// parameters both required and optional.
   CallStructure get callStructure {
     return new CallStructure(
         positionalParameters + namedParameters.length, namedParameters);
   }
 }