Normalize type masks to use the least upper instantiated subclass/type.

pkg/compiler/lib/src/closure.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.
 
 library closureToClassMapper;
 
 import 'common.dart';
 import 'common/names.dart' show
     Identifiers;
 import 'common/resolution.dart' show
@@ skipping 980 matching lines @@
     return sb.toString();
   }
 
   JavaScriptBackend get backend => compiler.backend;
 
   ClosureClassMap globalizeClosure(FunctionExpression node,
                                    LocalFunctionElement element) {
     String closureName = computeClosureName(element);
     ClosureClassElement globalizedElement = new ClosureClassElement(
         node, closureName, compiler, element);
+    // Extend [globalizedElement] as an instantiated class in the closed world.
+    compiler.world.registerClass(
+        globalizedElement, isDirectlyInstantiated: true);
     FunctionElement callElement =
         new SynthesizedCallMethodElementX(Identifiers.call,
                                           element,
                                           globalizedElement);
     backend.maybeMarkClosureAsNeededForReflection(
         globalizedElement, callElement, element);
     MemberElement enclosing = element.memberContext;
     enclosing.nestedClosures.add(callElement);
     globalizedElement.addMember(callElement, reporter);
     globalizedElement.computeAllClassMembers(compiler);
@@ skipping 116 matching lines @@
 
   String get name => typeVariable.name;
 
   int get hashCode => typeVariable.hashCode;
 
   bool operator ==(other) {
     if (other is! TypeVariableLocal) return false;
     return typeVariable == other.typeVariable;
   }
 }