Store named parameters in sorted lists instead of using maps.

lib/type_environment.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_environment;
 
 import 'ast.dart';
 import 'class_hierarchy.dart';
 import 'core_types.dart';
 import 'type_algebra.dart';
 
@@ skipping 188 matching lines @@
       return false;
     }
     for (int i = 0; i < supertype.positionalParameters.length; ++i) {
       var supertypeParameter = supertype.positionalParameters[i];
       var subtypeParameter = subtype.positionalParameters[i];
       // Termination: Both types shrink in size.
       if (!isSubtypeOf(supertypeParameter, subtypeParameter)) {
         return false;
       }
     }
-    for (String name in supertype.namedParameters.keys) {
-      var supertypeParameter = supertype.namedParameters[name];
-      var subtypeParameter = subtype.namedParameters[name];
-      if (subtypeParameter == null) return false;
+    int subtypeNameIndex = 0;
+    for (NamedType supertypeParameter in supertype.namedParameters) {
+      while (subtypeNameIndex < subtype.namedParameters.length &&
+          subtype.namedParameters[subtypeNameIndex].name !=
+              supertypeParameter.name) {
+        ++subtypeNameIndex;
+      }
+      if (subtypeNameIndex == subtype.namedParameters.length) return false;
+      NamedType subtypeParameter = subtype.namedParameters[subtypeNameIndex];
       // Termination: Both types shrink in size.
-      if (!isSubtypeOf(supertypeParameter, subtypeParameter)) {
+      if (!isSubtypeOf(supertypeParameter.type, subtypeParameter.type)) {
         return false;
       }
     }
     return true;
   }
 }