First stab at parsing redirecting constructors.

lib/compiler/implementation/resolver.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.
 
 abstract class TreeElements {
   Element operator[](Node node);
   Selector getSelector(Send send);
   DartType getType(TypeAnnotation annotation);
   bool isParameterChecked(Element element);
 }
@@ skipping 1609 matching lines @@
     for (Link<Node> link = node.nodes; !link.isEmpty(); link = link.tail) {
       visit(link.head);
     }
   }
 
   visitOperator(Operator node) {
     unimplemented(node, 'operator');
   }
 
   visitReturn(Return node) {
+    if (node.firstTokenStringValue === '=') {
+      unimplemented(node, 'redirecting constructors');
+    }
     visit(node.expression);
   }
 
   visitThrow(Throw node) {
     visit(node.expression);
   }
 
   visitVariableDefinitions(VariableDefinitions node) {
     visit(node.type);
     VariableDefinitionsVisitor visitor =
@@ skipping 1240 matching lines @@
 
   Element localLookup(SourceString name) => library.find(name);
   Element lookup(SourceString name) => localLookup(name);
   Element lexicalLookup(SourceString name) => localLookup(name);
 
   Element add(Element newElement) {
     throw "Cannot add an element in the top scope";
   }
   String toString() => '$element';
 }