Make arguments of MutationObserver named.

lib/html/src/Measurement.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.
 
 typedef Object ComputeValue();
 
 class _MeasurementRequest<T> {
   final ComputeValue computeValue;
   final Completer<T> completer;
   Object value;
@@ skipping 81 matching lines @@
  */
 class _MutationObserverScheduler extends _MeasurementScheduler {
   MutationObserver _observer;
   Element _dummy;
 
   _MutationObserverScheduler(_MeasurementCallback callback): super(callback) {
     // Mutation events get fired as soon as the current event stack is unwound
     // so we just make a dummy event and listen for that.
     _observer = new MutationObserver(this._handleMutation);
     _dummy = new DivElement();
-    // OPTIONALS _observer.observe(_dummy, attributes: true);
-    _observer.observe(_dummy, {}, null, true);
+    _observer.observe(_dummy, attributes: true);
   }
 
   void _schedule() {
     // Toggle it to trigger the mutation event.
     _dummy.hidden = !_dummy.hidden;
   }
 
   _handleMutation(List<MutationRecord> mutations, MutationObserver observer) {
     this._onCallback();
   }
@@ skipping 77 matching lines @@
     }
   }
 
   if (readyMeasurementFrameCallbacks !== null) {
     for (TimeoutHandler handler in readyMeasurementFrameCallbacks) {
       // TODO(jacobr): wrap each call to a handler in a try-catch block.
       handler();
     }
   }
 }