Make the ClosedWorld build the closure class on the kernel side.

pkg/compiler/lib/src/ssa/builder_kernel.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.
 
 import 'package:kernel/ast.dart' as ir;
 
 import '../closure.dart';
 import '../common.dart';
 import '../common/codegen.dart' show CodegenRegistry;
 import '../common/names.dart';
@@ skipping 117 matching lines @@
 
   HGraph build() {
     return reporter.withCurrentElement(localsMap.currentMember, () {
       // TODO(het): no reason to do this here...
       HInstruction.idCounter = 0;
       MemberDefinition definition =
           _elementMap.getMemberDefinition(targetElement);
 
       switch (definition.kind) {
         case MemberKind.regular:
+        case MemberKind.closureField:
         case MemberKind.closureCall:
           ir.Node target = definition.node;
           if (target is ir.Procedure) {
             _targetFunction = target.function;
             buildFunctionNode(_targetFunction);
           } else if (target is ir.Field) {
             if (handleConstantField(targetElement, registry, closedWorld)) {
               // No code is generated for `targetElement`: All references inline
               // the constant value.
               return null;
@@ skipping 3505 matching lines @@
     enterBlock.setBlockFlow(
         new HTryBlockInformation(
             kernelBuilder.wrapStatementGraph(bodyGraph),
             exception,
             kernelBuilder.wrapStatementGraph(catchGraph),
             kernelBuilder.wrapStatementGraph(finallyGraph)),
         exitBlock);
     kernelBuilder.inTryStatement = previouslyInTryStatement;
   }
 }