Changed to use JSInterop

tools/dom/templates/html/impl/impl_MutationObserver.darttemplate

 // 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 $LIBRARYNAME;
 
 $(ANNOTATIONS)$(NATIVESPEC)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS {
 $!MEMBERS
   /**
    * Checks to see if the mutation observer API is supported on the current
    * platform.
    */
   static bool get supported {
 $if DARTIUM
     return true;
 $else
     return JS('bool',
         '!!(window.MutationObserver || window.WebKitMutationObserver)');
 $endif
   }
+$if DARTIUM
+  @DocsEditable()
+$if JSINTEROP
+  static MutationObserver _create(callback) => wrap_jso(_blink.BlinkMutationObserver.instance.constructorCallback_1_((List<MutationRecord> mutations, MutationObserver observer) {
+      var wrapped_mutations = [];
+      for (var mutation in mutations) {
+        // Wrap the Javascript object for each MutationRecord.
+        wrapped_mutations.add(wrap_jso(mutation));
+      }
+      // Wrap the MutationObserver too.
+      callback(wrapped_mutations, wrap_jso(observer));
+  }));
+$else
+  static MutationObserver _create(callback) => _blink.BlinkMutationObserver.instance.constructorCallback_1_((List<MutationRecord> mutations, MutationObserver observer) {
+      var wrapped_mutations = [];
+      for (var mutation in mutations) {
+        // Wrap the Javascript object for each MutationRecord.
+        wrapped_mutations.add(wrap_jso(mutation));
+      }
+      // Wrap the MutationObserver too.
+      callback(wrapped_mutations, wrap_jso(observer));
+  });
+$endif
+$endif
 
   /**
    * Observes the target for the specified changes.
    *
    * Some requirements for the optional parameters:
    *
    * * Either childList, attributes or characterData must be true.
    * * If attributeOldValue is true then attributes must also be true.
    * * If attributeFilter is specified then attributes must be true.
    * * If characterDataOldValue is true then characterData must be true.
@@ skipping 63 matching lines @@
     return JS('MutationObserver',
         'new(window.MutationObserver||window.WebKitMutationObserver||'
         'window.MozMutationObserver)(#)',
         convertDartClosureToJS(_wrapBinaryZone(callback), 2));
   }
 $else
   factory MutationObserver(MutationCallback callback) =>
       new MutationObserver._(_wrapBinaryZone(callback));
 $endif
 }