Specialize the return type of a factory constructor to be the enclosing type.

sdk/lib/_internal/compiler/implementation/resolution/members.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 resolution;
 
 abstract class TreeElements {
   Element get currentElement;
   Set<Node> get superUses;
 
@@ skipping 3725 matching lines @@
           } else {
             compiler.onDeprecatedFeature(formalParameters, 'getter parameters');
           }
         }
       }
       LinkBuilder<Element> parametersBuilder =
         visitor.analyzeNodes(formalParameters.nodes);
       requiredParameterCount  = parametersBuilder.length;
       parameters = parametersBuilder.toLink();
     }
-    DartType returnType = compiler.resolveReturnType(element, returnNode);
+    DartType returnType = element.isFactoryConstructor()
+        ? element.getEnclosingClass().computeType(compiler)
+        : compiler.resolveReturnType(element, returnNode);
     if (element.isSetter() && (requiredParameterCount != 1 ||
                                visitor.optionalParameterCount != 0)) {
       // If there are no formal parameters, we already reported an error above.
       if (formalParameters != null) {
         compiler.reportErrorCode(formalParameters,
                                  MessageKind.ILLEGAL_SETTER_FORMALS);
       }
     }
     if (element.isGetter() && (requiredParameterCount != 0
                                || visitor.optionalParameterCount != 0)) {
@@ skipping 169 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }