Store named parameters in sorted lists instead of using maps.

lib/transformations/treeshaker.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.tree_shaker;
 
 import '../ast.dart';
 import '../class_hierarchy.dart';
 import '../core_types.dart';
 
@@ skipping 739 matching lines @@
         visitBivariant(typeArgument);
       }
     }
   }
 
   visitFunctionType(FunctionType node) {
     visit(node.returnType);
     for (int i = 0; i < node.positionalParameters.length; ++i) {
       visitContravariant(node.positionalParameters[i]);
     }
-    node.namedParameters.values.forEach(visitContravariant);
+    for (int i = 0; i < node.namedParameters.length; ++i) {
+      visitContravariant(node.namedParameters[i].type);
+    }
   }
 
   visitTypeParameterType(TypeParameterType node) {}
 
   /// Just treat a couple of whitelisted classes as having covariant type
   /// parameters.
   bool isWhitelistedCovariant(Class classNode) {
     if (classNode.typeParameters.isEmpty) return false;
     CoreTypes coreTypes = shaker.coreTypes;
     return classNode == coreTypes.iteratorClass ||
         classNode == coreTypes.iterableClass ||
         classNode == coreTypes.futureClass ||
         classNode == coreTypes.streamClass ||
         classNode == coreTypes.listClass ||
         classNode == coreTypes.mapClass;
   }
 }