Change final field to abstract getter.

lib/compiler/implementation/elements/elements.dart

 // Copyright (c) 2012, 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('elements');
 
 #import('../tree/tree.dart');
 #import('../scanner/scannerlib.dart');
 #import('../leg.dart');  // TODO(karlklose): we only need type.
 #import('../util/util.dart');
@@ skipping 827 matching lines @@
 abstract class TypeDeclarationElement implements Element {
   // TODO(johnniwinther): This class should eventually be a mixin.
 
   /**
    * The type variables declared on this declaration. The type variables are not
    * available until the type of the element has been computed through
    * [computeType].
    */
   // TODO(johnniwinther): Find a (better) way to decouple [typeVariables] from
   // [Compiler].
-  final Link<Type> typeVariables;
+  abstract Link<Type> get typeVariables();
 
   /**
    * Creates the type variables, their type and corresponding element, for the
    * type variables declared in [parameter] on [element]. The bounds of the type
    * variables are not set until [element] has been resolved.
    */
   static Link<Type> createTypeVariables(TypeDeclarationElement element,
                                         NodeList parameters) {
     if (parameters === null) return const EmptyLink<Type>();
 
@@ skipping 389 matching lines @@
   TypeVariableElement(name, Element enclosing, this.cachedNode,
                       [this.type, this.bound])
     : super(name, ElementKind.TYPE_VARIABLE, enclosing);
 
   TypeVariableType computeType(compiler) => type;
 
   Node parseNode(compiler) => cachedNode;
 
   String toString() => "${enclosingElement.toString()}.${name.slowToString()}";
 }