Clean up the timer source in the isolate library to be less VM specific.

sdk/lib/isolate/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.
 
 abstract class Timer {
   /**
    * Creates a new timer. The [callback] callback is invoked after
    * [milliSeconds] milliseconds.
    */
-  factory Timer(int milliSeconds, void callback(Timer timer)) {
-    if (_TimerFactory._factory == null) {
-      throw new UnsupportedError("Timer interface not supported.");
-    }
-    return _TimerFactory._factory(milliSeconds, callback, false);
-  }
+  external factory Timer(int milliSeconds, void callback(Timer timer));
 
   /**
    * Creates a new repeating timer. The [callback] is invoked every
    * [milliSeconds] millisecond until cancelled.
    */
-  factory Timer.repeating(int milliSeconds, void callback(Timer timer)) {
-    if (_TimerFactory._factory == null) {
-      throw new UnsupportedError("Timer interface not supported.");
-    }
-    return _TimerFactory._factory(milliSeconds, callback, true);
-  }
+  external factory Timer.repeating(int milliSeconds,
+                                   void callback(Timer timer));
 
   /**
    * Cancels the timer.
    */
   void cancel();
 }
-
-// TODO(ajohnsen): Patch timer once we have support for patching named
-//                 factory constructors in the VM.
-
-typedef Timer _TimerFactoryClosure(int milliSeconds,
-                                   void callback(Timer timer),
-                                   bool repeating);
-
-class _TimerFactory {
-  static _TimerFactoryClosure _factory;
-}
-
-// TODO(ahe): Warning: this is NOT called by Dartium. Instead, it sets
-// [_TimerFactory._factory] directly.
-void _setTimerFactoryClosure(_TimerFactoryClosure closure) {
-  _TimerFactory._factory = closure;
-}