Fix a spurious warning in Frog selfhost

frog/var_member.dart

 // Copyright (c) 2011, 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.
 
 /** A dynamic member stub. */
 class VarMember {
   final String name;
 
   VarMember(this.name);
 
@@ skipping 179 matching lines @@
   /** Invokes members to ensure they're generated. */
   _invokeMembers(MethodGenerator context, Node node) {
     if (_fallbackStubs != null) return;
 
     var objectStub = null;
     _fallbackStubs = [];
     for (var member in members) {
       // Invoke the member with the stub args (this gives us the method body),
       // then create the stub method.
       final target = new Value(member.declaringType, 'this', node.span);
-      var result = member.invoke(context, node, target, args);
+      var result = member.invoke(context, node, target, args, isDynamic:true);
       var stub = new VarMethodStub(name, member, args, result);
 
       // Put the stub on the type directly if possible. Otherwise
       // put the stub on Object.prototype.
       var type = member.declaringType;
       if (type.isObject) {
         objectStub = stub;
       } else if (type.library != world.dom) {
         _addVarStub(type, stub);
       } else {
@@ skipping 50 matching lines @@
   }
 }
 
 String _getCallStubName(String name, Arguments args) {
   final nameBuilder = new StringBuffer('${name}\$${args.bareCount}');
   for (int i = args.bareCount; i < args.length; i++) {
     nameBuilder.add('\$').add(args.getName(i));
   }
   return nameBuilder.toString();
 }