Remove requiredTypes

pkg/compiler/lib/src/resolution/variables.dart

 // Copyright (c) 2015, 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 dart2js.resolution.variables;
 
 import '../common.dart';
 import '../compiler.dart' show
     Compiler;
 import '../elements/modelx.dart' show
@@ skipping 36 matching lines @@
     if (scope.variableReferencedInInitializer) {
       reporter.reportErrorMessage(
           identifier, MessageKind.REFERENCE_IN_INITIALIZATION,
           {'variableName': name});
     }
     return identifier;
   }
 
   Identifier visitIdentifier(Identifier node) {
     // The variable is initialized to null.
-    registry.registerInstantiatedClass(compiler.nullClass);
+    registry.registerInstantiatedType(compiler.coreTypes.nullType);
     if (definitions.modifiers.isConst) {
       reporter.reportErrorMessage(
           node, MessageKind.CONST_WITHOUT_INITIALIZER);
     }
     if (definitions.modifiers.isFinal &&
         !resolver.allowFinalWithoutInitializer) {
       reporter.reportErrorMessage(
           node, MessageKind.FINAL_WITHOUT_INITIALIZER);
     }
     return node;
   }
 
   visitNodeList(NodeList node) {
     for (Link<Node> link = node.nodes; !link.isEmpty; link = link.tail) {
       Identifier name = visit(link.head);
       LocalVariableElementX element = new LocalVariableElementX(
           name.source, resolver.enclosingElement,
           variables, name.token);
       resolver.defineLocalVariable(link.head, element);
       resolver.addToScope(element);
       if (definitions.modifiers.isConst) {
         compiler.enqueuer.resolution.addDeferredAction(element, () {
           element.constant =
               compiler.resolver.constantCompiler.compileConstant(element);
         });
       }
     }
   }
 }