Fix some issues after introducing NamedType.

testcases/input/named_parameters.dart

 // Copyright (c) 2016, 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.
 class Superclass {
   foo({alpha, beta}) {}
   bar({beta, alpha}) {}
 
-  namedCallback(callback({alpha, beta})) {}
+  namedCallback(callback({String alpha, int beta})) {
+    callback(alpha: 'one', beta: 2);
+    callback(beta: 1, alpha: 'two');
+  }
 }
 
 class Subclass extends Superclass {
   foo({beta, alpha}) {}
   bar({alpha, beta}) {}
 
-  namedCallback(callback({beta, alpha})) {}
+  namedCallback(callback({int beta, String alpha})) {}
 }
 
 topLevelNamed(beta, alpha, {gamma, delta}) {}
 topLevelOptional(beta, alpha, [gamma, delta]) {}
 
 main() {
   new Subclass().foo(beta: 1, alpha: 2);
   new Subclass().foo(alpha: 1, beta: 2);
   topLevelNamed(1, 2, gamma: 3, delta: 4);
   topLevelNamed(1, 2, delta: 3, gamma: 4);
 }