Infer VariableSet types.

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.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.
 
 /// This file declares a "shadow hierarchy" of concrete classes which extend
 /// the kernel class hierarchy, adding methods and fields needed by the
 /// BodyBuilder.
 ///
 /// Instances of these classes may be created using the factory methods in
 /// `ast_factory.dart`.
@@ skipping 866 matching lines @@
       // KernelVariableDeclaration.
       mutatedInClosure = true;
       declaredType = variable.type;
     }
     return inferrer.inferVariableGet(typeContext, typeNeeded, mutatedInClosure,
         _fact, _scope, fileOffset, declaredType, (type) {
       promotedType = type;
     });
   }
 }
+
+/// Concrete shadow object representing a write to a variable in kernel form.
+class KernelVariableSet extends VariableSet implements KernelExpression {
+  KernelVariableSet(VariableDeclaration variable, Expression value)
+      : super(variable, value);
+
+  @override
+  DartType _inferExpression(
+      KernelTypeInferrer inferrer, DartType typeContext, bool typeNeeded) {
+    var variable = this.variable as KernelVariableDeclaration;
+    return inferrer.inferVariableSet(
+        typeContext, typeNeeded, variable._declaredType, value);
+  }
+}