Fix for resolving interface constructors in factory, issue 521.

tests/language/src/ClassTest.dart

 // Copyright (c) 2011, 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.
 
 // Tests basic classes and methods.
 class ClassTest {
   ClassTest() {}
 
   static testMain() {
     var test = new ClassTest();
@@ skipping 87 matching lines @@
 }
 
 class Sup implements Inter {
   int x_;
   int k_;
 
   factory Sup.named() {
     return new Sub();
   }
 
-  factory Inter.factory() {
+  factory Sup.factory() {
     return new Sub();
   }
 
   Sup.fromInt(int x) {
     x_ = x;
     k_ = 0;
   }
 
   int methodX() {
     return x_;
@@ skipping 42 matching lines @@
   }
 
   Sub() : super(42) {
     y_ = 0;
   }
 }
 
 main() {
   ClassTest.testMain();
 }