Codegen support for the argument definition test.

lib/compiler/implementation/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 visitCascade(Cascade node);
   R visitCascadeReceiver(CascadeReceiver node);
   R visitCaseMatch(CaseMatch node);
@@ skipping 264 matching lines @@
   bool get isFunctionObjectInvocation => selector === null;
   bool get isPrefix => argumentsNode is Prefix;
   bool get isPostfix => argumentsNode is Postfix;
   bool get isCall => !isOperator && !isPropertyAccess;
   bool get isIndex =>
       isOperator && selector.asOperator().source.stringValue === '[]';
   bool get isLogicalAnd =>
       isOperator && selector.asOperator().source.stringValue === '&&';
   bool get isLogicalOr =>
       isOperator && selector.asOperator().source.stringValue === '||';
+  bool get isParameterCheck =>
+      isOperator && selector.asOperator().source.stringValue === '?';
 
   Token getBeginToken() {
     if (isPrefix && !isIndex) return selector.getBeginToken();
     return firstBeginToken(receiver, selector);
   }
 
   Token getEndToken() {
     if (isPrefix) {
       if (receiver !== null) return receiver.getEndToken();
       if (selector !== null) return selector.getEndToken();
@@ skipping 1472 matching lines @@
  * argument).
  *
  * TODO(ahe): This method is controversial, the team needs to discuss
  * if top-level methods are acceptable and what naming conventions to
  * use.
  */
 initializerDo(Node node, f(Node node)) {
   SendSet send = node.asSendSet();
   if (send !== null) return f(send.arguments.head);
 }