Change StreamController constructor.

tools/dom/templates/html/impl/impl_Geolocation.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;
 
 @DocsEditable
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
 
   @DomName('Geolocation.getCurrentPosition')
@@ skipping 36 matching lines @@
     if (timeout != null) {
       options['timeout'] = timeout.inMilliseconds;
     }
     if (maximumAge != null) {
       options['maximumAge'] = maximumAge.inMilliseconds;
     }
 
     int watchId;
     var controller;
     controller = new StreamController<Geoposition>(
-      onSubscriptionStateChange: () {
-        if (controller.hasListener) {
-          assert(watchId == null);
-          watchId = $dom_watchPosition(
-              (position) {
-                controller.add(_ensurePosition(position));
-              },
-              (error) {
-                controller.addError(error);
-              },
-              options);
-        } else {
-          assert(watchId != null);
-          $dom_clearWatch(watchId);
-        }
+      onListen: () {
+        assert(watchId == null);
+        watchId = $dom_watchPosition(
+            (position) {
+              controller.add(_ensurePosition(position));
+            },
+            (error) {
+              controller.addError(error);
+            },
+            options);
+      },
+      onCancel: () {
+        assert(watchId != null);
+        $dom_clearWatch(watchId);
       });
 
     return controller.stream;
   }
 
   Geoposition _ensurePosition(domPosition) {
 $if DART2JS
     try {
       // Firefox may throw on this.
       if (domPosition is Geoposition) {
@@ skipping 17 matching lines @@
 class _GeopositionWrapper implements Geoposition {
   var _ptr;
   _GeopositionWrapper(this._ptr);
 
   Coordinates get coords => JS('Coordinates', '#.coords', _ptr);
   int get timestamp => JS('int', '#.timestamp', _ptr);
 }
 $endif