Make sure to bind a method to its receiver if it is stored in a temporary.

pkg/js_ast/lib/src/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.
 
 part of js_ast;
 
 abstract class NodeVisitor<T> {
   T visitProgram(Program node);
 
   T visitBlock(Block node);
@@ skipping 225 matching lines @@
 
   accept(NodeVisitor visitor) => visitor.visitBlock(this);
   void visitChildren(NodeVisitor visitor) {
     for (Statement statement in statements) statement.accept(visitor);
   }
   Block _clone() => new Block(statements);
 }
 
 class ExpressionStatement extends Statement {
   final Expression expression;
-  ExpressionStatement(this.expression);
+  ExpressionStatement(this.expression) {
+    assert(this.expression != null);
+  }
 
   accept(NodeVisitor visitor) => visitor.visitExpressionStatement(this);
   void visitChildren(NodeVisitor visitor) { expression.accept(visitor); }
   ExpressionStatement _clone() => new ExpressionStatement(expression);
 }
 
 class EmptyStatement extends Statement {
   EmptyStatement();
 
   accept(NodeVisitor visitor) => visitor.visitEmptyStatement(this);
@@ skipping 913 matching lines @@
 class Comment extends Statement {
   final String comment;
 
   Comment(this.comment);
 
   accept(NodeVisitor visitor) => visitor.visitComment(this);
   Comment _clone() => new Comment(comment);
 
   void visitChildren(NodeVisitor visitor) {}
 }