Adding annotation for partial browser support and example implementation for MutationObservers.

sdk/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.
 
 part of html;
 
 typedef Object ComputeValue();
 
 class _MeasurementRequest<T> {
   final ComputeValue computeValue;
   final Completer<T> completer;
   Object value;
   bool exception = false;
   _MeasurementRequest(this.computeValue, this.completer);
 }
 
 typedef void _MeasurementCallback();
 
-
 /**
  * This class attempts to invoke a callback as soon as the current event stack
  * unwinds, but before the browser repaints.
  */
 abstract class _MeasurementScheduler {
   bool _nextMeasurementFrameScheduled = false;
   _MeasurementCallback _callback;
 
   _MeasurementScheduler(this._callback);
 
   /**
    * Creates the best possible measurement scheduler for the current platform.
    */
   factory _MeasurementScheduler.best(_MeasurementCallback callback) {
-    if (_isMutationObserverSupported()) {
+    if (MutationObserver.supported) {
       return new _MutationObserverScheduler(callback);
     }
     return new _PostMessageScheduler(callback);
   }
 
   /**
    * Schedules a measurement callback if one has not been scheduled already.
    */
   void maybeSchedule() {
     if (this._nextMeasurementFrameScheduled) {
@@ skipping 147 matching lines @@
     }
   }
 
   if (readyMeasurementFrameCallbacks != null) {
     for (TimeoutHandler handler in readyMeasurementFrameCallbacks) {
       // TODO(jacobr): wrap each call to a handler in a try-catch block.
       handler();
     }
   }
 }