Infer VariableSet types.

pkg/front_end/lib/src/fasta/kernel/kernel_ast_factory.dart

 // Copyright (c) 2017, 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:front_end/src/fasta/kernel/utils.dart';
 import 'package:front_end/src/fasta/scanner/token.dart' show Token;
 import 'package:front_end/src/fasta/type_inference/type_promotion.dart';
 import 'package:kernel/ast.dart';
 
 import '../builder/ast_factory.dart';
@@ skipping 231 matching lines @@
 
   @override
   VariableGet variableGet(
       VariableDeclaration variable,
       TypePromotionFact<VariableDeclaration> fact,
       TypePromotionScope scope,
       Token token) {
     return new KernelVariableGet(variable, fact, scope)
       ..fileOffset = offsetForToken(token);
   }
+
+  @override
+  VariableSet variableSet(VariableDeclaration variable, Expression value) {
+    return new KernelVariableSet(variable, value);
+  }
 }