Move JSSyntaxRegExp to core as a private member. This removes the last refrences to dart:coreimpl.

samples/swarm/swarm_ui_lib/observable/observable.dart

 // Copyright (c) 2011, 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.
 
 library observable;
 
-import 'dart:coreimpl';
-
 part 'ChangeEvent.dart';
 part 'EventBatch.dart';
 
 /**
  * An object whose changes are tracked and who can issue events notifying how it
  * has been changed.
  */
 abstract class Observable {
   /** Returns a globally unique identifier for the object. */
   // TODO(sigmund): remove once dart supports maps with arbitrary keys.
@@ skipping 268 matching lines @@
     // Only fire on an actual change.
     if (!identical(newValue, _value)) {
       final oldValue = _value;
       _value = newValue;
       recordPropertyUpdate("value", newValue, oldValue);
     }
   }
 
   T _value;
 }