Resolve initializers in their proper scope.

dart/frog/leg/tree/nodes.dart

 // Copyright (c) 2012, 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.
 
 interface Visitor<R> {
   R visitBlock(Block node);
   R visitBreakStatement(BreakStatement node);
   R visitCatchBlock(CatchBlock node);
   R visitClassNode(ClassNode node);
   R visitConditional(Conditional node);
@@ skipping 1610 matching lines @@
   DartString visitLiteralString(LiteralString node) => node.dartString;
 }
 
 class IsInterpolationVisitor extends AbstractVisitor<bool> {
   const IsInterpolationVisitor();
   bool visitNode(Node node) => false;
   bool visitStringInterpolation(StringInterpolation node) => true;
   bool visitStringJuxtaposition(StringJuxtaposition node)
       => node.isInterpolation;
 }
+
+/**
+ * If the given node is a send set, it visits its initializer (first
+ * argument).
+ */
+initializerDo(Node node, f(Node node)) {
+  SendSet send = node.asSendSet();
+  if (send !== null) return f(send.arguments.head);
+}