Fix some issues after introducing NamedType.

lib/type_checker.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.
 library kernel.type_checker;
 
 import 'ast.dart';
 import 'class_hierarchy.dart';
 import 'core_types.dart';
 import 'type_algebra.dart';
 import 'type_environment.dart';
@@ skipping 453 matching lines @@
     var instantiation =
         Substitution.fromPairs(function.typeParameters, arguments.types);
     for (int i = 0; i < arguments.positional.length; ++i) {
       var expectedType = instantiation.substituteType(
           function.positionalParameters[i],
           contravariant: true);
       checkAssignableExpression(arguments.positional[i], expectedType);
     }
     for (int i = 0; i < arguments.named.length; ++i) {
       var argument = arguments.named[i];
-      var expectedType = function.namedParameters[argument.name];
-      if (expectedType == null) {
+      bool found = false;
+      for (int j = 0; j < function.namedParameters.length; ++j) {
+        if (argument.name == function.namedParameters[j].name) {
+          var expectedType = instantiation.substituteType(
+              function.namedParameters[j].type,
+              contravariant: true);
+          checkAssignableExpression(argument.value, expectedType);
+          found = true;
+          break;
+        }
+      }
+      if (!found) {
         fail(argument.value, 'Unexpected named parameter: ${argument.name}');
-      } else {
-        checkAssignableExpression(argument.value,
-            instantiation.substituteType(expectedType, contravariant: true));
+        return const BottomType();
       }
     }
     return instantiation.substituteType(function.returnType);
   }
 
   @override
   DartType visitMethodInvocation(MethodInvocation node) {
     var target = node.interfaceTarget;
     if (target == null) {
       var receiver = visitExpression(node.receiver);
@@ skipping 356 matching lines @@
   }
 
   @override
   visitLocalInitializer(LocalInitializer node) {
     visitVariableDeclaration(node.variable);
   }
 
   @override
   visitInvalidInitializer(InvalidInitializer node) {}
 }