Add visitor methods specific to ??= to SemanticSendVisitor.

pkg/compiler/lib/src/inferrer/inferrer_visitor.dart

 // Copyright (c) 2013, 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 inferrer_visitor;
 
 import 'dart:collection' show
     IterableMixin;
 
 import '../compiler.dart' show
@@ skipping 674 matching lines @@
   void updateField(Element element, T type) {
     fieldScope.updateField(element, type);
   }
 }
 
 abstract class InferrerVisitor<T, E extends MinimalInferrerEngine<T>>
     extends Visitor<T>
     with SendResolverMixin,
          SemanticSendResolvedMixin<T, dynamic>,
          CompoundBulkMixin<T, dynamic>,
+         SetIfNullBulkMixin<T, dynamic>,
          PrefixBulkMixin<T, dynamic>,
          PostfixBulkMixin<T, dynamic>,
          ErrorBulkMixin<T, dynamic>,
          NewBulkMixin<T, dynamic>,
          SetBulkMixin<T, dynamic>
     implements SemanticSendVisitor<T, dynamic> {
   final Compiler compiler;
   final AstElement analyzedElement;
   final TypeSystem<T> types;
   final E inferrer;
@@ skipping 61 matching lines @@
   T bulkHandleSet(SendSet node, _) {
     return handleSendSet(node);
   }
 
   @override
   T bulkHandleCompound(SendSet node, _) {
     return handleSendSet(node);
   }
 
   @override
+  T bulkHandleSetIfNull(SendSet node, _) {
+    return handleSendSet(node);
+  }
+
+  @override
   T bulkHandlePrefix(SendSet node, _) {
     return handleSendSet(node);
   }
 
   @override
   T bulkHandlePostfix(SendSet node, _) {
     return handleSendSet(node);
   }
 
   @override
@@ skipping 741 matching lines @@
     return type;
   }
 
   T visitCascade(Cascade node) {
     // Ignore the result of the cascade send and return the type of the cascade
     // receiver.
     visit(node.expression);
     return cascadeReceiverStack.removeLast();
   }
 }