Support type variables on redirecting factory constructors.

sdk/lib/_internal/compiler/implementation/tree/nodes.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.
 
 part of tree;
 
 abstract class Visitor<R> {
   const Visitor();
 
   R visitNode(Node node);
@@ skipping 675 matching lines @@
 
   FunctionExpression(this.name, this.parameters, this.body, this.returnType,
                      this.modifiers, this.initializers, this.getOrSet) {
     assert(modifiers != null);
   }
 
   FunctionExpression asFunctionExpression() => this;
 
   accept(Visitor visitor) => visitor.visitFunctionExpression(this);
 
+  bool get isRedirectingFactory {
+    return body != null && body.asReturn() != null &&
+        body.asReturn().isRedirectingFactoryBody;
+  }
+
   visitChildren(Visitor visitor) {
     if (modifiers != null) modifiers.accept(visitor);
     if (returnType != null) returnType.accept(visitor);
     if (name != null) name.accept(visitor);
     if (parameters != null) parameters.accept(visitor);
     if (initializers != null) initializers.accept(visitor);
     if (body != null) body.accept(visitor);
   }
 
   bool hasBody() => body.asEmptyStatement() == null;
@@ skipping 1356 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send != null) return f(send.arguments.head);
 }