Support type variables on redirecting factory constructors.

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 operator[](Node node);
   Selector getSelector(Send send);
   DartType getType(Node node);
@@ skipping 2230 matching lines @@
       compiler.reportMessage(
           compiler.spanFromSpannable(node),
           MessageKind.FACTORY_REDIRECTION_IN_NON_FACTORY.error([]),
           Diagnostic.ERROR);
       compiler.reportMessage(
           compiler.spanFromSpannable(enclosingElement),
           MessageKind.MISSING_FACTORY_KEYWORD.error([]),
           Diagnostic.INFO);
     }
     Element redirectionTarget = resolveRedirectingFactory(node);
-    var type = mapping.getType(node.expression);
-    if (type is InterfaceType && !type.isRaw) {
-      unimplemented(node.expression, 'type arguments on redirecting factory');
-    }
     useElement(node.expression, redirectionTarget);
     FunctionElement constructor = enclosingElement;
     if (constructor.modifiers.isConst() &&
         !redirectionTarget.modifiers.isConst()) {
       error(node, MessageKind.CONSTRUCTOR_IS_NOT_CONST);
     }
     constructor.defaultImplementation = redirectionTarget;
     if (Elements.isUnresolved(redirectionTarget)) return;
 
     // TODO(ahe): Check that this doesn't lead to a cycle.  For now,
@@ skipping 1338 matching lines @@
     return e;
   }
 
   /// Assumed to be called by [resolveRedirectingFactory].
   Element visitReturn(Return node) {
     Node expression = node.expression;
     return finishConstructorReference(visit(expression),
                                       expression, expression);
   }
 }