Fix type annotation, spotted by checked mode.

lib/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.
 
 class EnqueueTask extends CompilerTask {
   final Enqueuer codegen;
   final Enqueuer resolution;
 
   String get name => 'Enqueue';
 
@@ skipping 57 matching lines @@
       seenClasses = new Set<ClassElement>(),
       universe = new Universe(),
       queue = new Queue<WorkItem>(),
       resolvedElements = new Map<Element, TreeElements>(),
       recompilationCandidates =
           new RecompilationQueue(itemCompilationContextCreator);
 
   bool get isResolutionQueue => compiler.enqueuer.resolution === this;
 
   TreeElements getCachedElements(Element element) {
+    // TODO(ngeoffray): Get rid of this check.
     if (element.enclosingElement.isClosure()) {
-      ClosureClassElement cls = element.enclosingElement;
+      closureMapping.ClosureClassElement cls = element.enclosingElement;
       element = cls.methodElement;
     }
     Element owner = element.getOutermostEnclosingMemberOrTopLevel();
     return compiler.enqueuer.resolution.resolvedElements[owner];
   }
 
   String lookupCode(Element element) =>
       universe.generatedCode[element].toString();
 
   void addToWorkList(Element element, [TreeElements elements]) {
@@ skipping 261 matching lines @@
   void registerIsCheck(Element element) {
     universe.isChecks.add(element);
   }
 
   void forEach(f(WorkItem work)) {
     while (!queue.isEmpty()) {
       f(queue.removeLast()); // TODO(kasperl): Why isn't this removeFirst?
     }
   }
 }