Forget closure classes.

dart/sdk/lib/_internal/compiler/implementation/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.
 
 part of dart2js;
 
 typedef ItemCompilationContext ItemCompilationContextCreator();
 
 class EnqueueTask extends CompilerTask {
   final ResolutionEnqueuer resolution;
@@ skipping 633 matching lines @@
     nativeEnqueuer.logSummary(log);
   }
 
   /// Log summary specific to the concrete enqueuer.
   void _logSpecificSummary(log(message));
 
   String toString() => 'Enqueuer($name)';
 
   void forgetElement(Element element) {
     universe.forgetElement(element, compiler);
+    seenClasses.remove(element);
   }
 }
 
 /// [Enqueuer] which is specific to resolution.
 class ResolutionEnqueuer extends Enqueuer {
   /**
    * Map from declaration elements to the [TreeElements] object holding the
    * resolution mapping for the element implementation.
    *
    * Invariant: Key elements are declaration elements.
@@ skipping 253 matching lines @@
   void processWorkItem(void f(WorkItem work), WorkItem work) {
     f(work);
   }
 }
 
 void removeFromSet(Map<String, Set<Element>> map, Element element) {
   Set<Element> set = map[element.name];
   if (set == null) return;
   set.remove(element);
 }