Revert "Zone support for Futures."

sdk/lib/async/timer.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 dart.async;
 
 abstract class Timer {
 
   /**
    * Creates a new timer.
@@ skipping 11 matching lines @@
    *     const ms = const Duration(milliseconds: 1);
    *
    *     startTimeout([int milliseconds]) {
    *       var duration = milliseconds == null ? TIMEOUT : ms * milliseconds;
    *       return new Timer(duration, handleTimeout);
    *     }
    *
    * Note: If Dart code using Timer is compiled to JavaScript, the finest
    * granularity available in the browser is 4 milliseconds.
    */
-  factory Timer(Duration duration, void callback()) {
-    return _Zone.current.createTimer(duration, callback);
-  }
+  external factory Timer(Duration duration, void callback());
 
   /**
    * Creates a new repeating timer.
    *
    * The [callback] is invoked repeatedly with [duration] intervals until
    * canceled. A negative duration is treated similar to a duration of 0.
    */
-  factory Timer.periodic(Duration duration,
-                                  void callback(Timer timer)) {
-    return _Zone.current.createPeriodicTimer(duration, callback);
-  }
+  external factory Timer.periodic(Duration duration,
+                                  void callback(Timer timer));
 
   /**
    * Runs the given [callback] asynchronously as soon as possible.
    *
    * This function is equivalent to `new Timer(Duration.ZERO, callback)`.
    */
   static void run(void callback()) {
     new Timer(Duration.ZERO, callback);
   }
 
   /**
    * Cancels the timer.
    */
   void cancel();
 }
-
-external Timer _createTimer(Duration duration, void callback());
-external Timer _createPeriodicTimer(Duration duration,
-                                    void callback(Timer timer));