Avoid using Invalid{Statement,Expression,Initializer}.

pkg/front_end/lib/src/fasta/kernel/fasta_accessors.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 fasta.fasta_accessors;
 
-export 'frontend_accessors.dart' show wrapInvalid;
-
 import 'package:front_end/src/fasta/kernel/kernel_shadow_ast.dart'
     show KernelArguments, KernelMethodInvocation;
 
 import 'package:front_end/src/fasta/kernel/utils.dart' show offsetForToken;
 
 import 'package:front_end/src/scanner/token.dart' show Token;
 
 import 'frontend_accessors.dart' show Accessor, buildIsNull, makeLet;
 
 import 'package:front_end/src/fasta/type_inference/type_promotion.dart'
@@ skipping 856 matching lines @@
             new NullLiteral(),
             new KernelMethodInvocation(
                 new VariableGet(variable), name, arguments)
               ..fileOffset = offset,
             const DynamicType()));
   } else {
     return new KernelMethodInvocation(receiver, name, arguments)
       ..fileOffset = offset;
   }
 }