Support for "a is Function".

frog/leg/enqueue.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.
 
 class EnqueueTask extends CompilerTask {
   EnqueueTask(Compiler compiler) : super(compiler);
   String get name() => 'Enqueue';
 
   void enqueueInvokedInstanceMethods() {
     // TODO(floitsch): find a more efficient way of doing this.
@@ skipping 45 matching lines @@
       if (selectors != null) {
         for (Selector selector in selectors) {
           if (selector.applies(compiler, member)) {
             return compiler.addToWorkList(member);
           }
         }
       }
       // If there is a property access with the same name as a method we
       // need to emit the method.
       if (compiler.universe.invokedGetters.contains(member.name)) {
+        // We will emit a closure, so make sure the closure class is
+        // generated.
+        compiler.closureClass.ensureResolved(compiler);
+        compiler.registerInstantiatedClass(compiler.closureClass);
         return compiler.addToWorkList(member);
       }
     } else if (member.kind == ElementKind.GETTER) {
       if (compiler.universe.invokedGetters.contains(member.name)) {
         return compiler.addToWorkList(member);
       }
       // A method invocation like in o.foo(x, y) might actually be an
       // invocation of the getter foo followed by an invocation of the
       // returned closure.
       Set<Selector> invokedSelectors =
@@ skipping 14 matching lines @@
     measure(() {
       cls.members.forEach((member) {
         if (member.kind === ElementKind.GETTER ||
             member.kind === ElementKind.FIELD) {
           compiler.universe.instantiatedClassInstanceFields.add(member.name);
         }
       });
     });
   }
 }