Avoid counting custom elements as added due to mirrors

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 67 matching lines @@
   bool queueIsClosed = false;
   EnqueueTask task;
   native.NativeEnqueuer nativeEnqueuer;  // Set by EnqueueTask
 
   bool hasEnqueuedEverything = false;
   bool hasEnqueuedReflectiveStaticFields = false;
 
   Enqueuer(this.name, this.compiler, this.itemCompilationContextCreator);
 
   Queue<WorkItem> get queue;
+  bool get queueIsEmpty => queue.isEmpty;
 
   /// Returns [:true:] if this enqueuer is the resolution enqueuer.
   bool get isResolutionQueue => false;
 
   /// Returns [:true:] if [member] has been processed by this enqueuer.
   bool isProcessed(Element member);
 
   /**
    * Documentation wanted -- johnniwinther
    *
@@ skipping 656 matching lines @@
     }
     CodegenWorkItem workItem = new CodegenWorkItem(
         element, itemCompilationContextCreator());
     queue.add(workItem);
   }
 
   void _logSpecificSummary(log(message)) {
     log('Compiled ${generatedCode.length} methods.');
   }
 }