Revert zone tasks.

tools/dom/src/shared_html.dart

 // Copyright (c) 2013, 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.dom.html;
 
-ZoneUnaryCallback/*<R, T>*/ _registerZone/*<R, T>*/(Zone zone,
-    ZoneUnaryCallback/*<R, T>*/ callback) {
-  // For performance reasons avoid registering if we are in the root zone.
-  if (identical(zone, Zone.ROOT)) return callback;
+// TODO(jacobr): remove these typedefs when dart:async supports generic types.
+typedef R _wrapZoneCallback<A, R>(A a);
+typedef R _wrapZoneBinaryCallback<A, B, R>(A a, B b);
+
+_wrapZoneCallback/*<A, R>*/ _wrapZone/*<A, R>*/(_wrapZoneCallback/*<A, R>*/ callback) {
+  // For performance reasons avoid wrapping if we are in the root zone.
+  if (Zone.current == Zone.ROOT) return callback;
   if (callback == null) return null;
-  return zone.registerUnaryCallback(callback);
+  // TODO(jacobr): we cast to _wrapZoneCallback/*<A, R>*/ to hack around missing
+  // generic method support in zones.
+  // ignore: STRONG_MODE_DOWN_CAST_COMPOSITE
+  _wrapZoneCallback/*<A, R>*/ wrapped =
+      Zone.current.bindUnaryCallback(callback, runGuarded: true);
+  return wrapped;
 }
 
-ZoneUnaryCallback/*<R, T>*/ _wrapZone/*<R, T>*/(ZoneUnaryCallback/*<R, T>*/ callback) {
-  // For performance reasons avoid wrapping if we are in the root zone.
-  if (identical(Zone.current, Zone.ROOT)) return callback;
+_wrapZoneBinaryCallback/*<A, B, R>*/ _wrapBinaryZone/*<A, B, R>*/(_wrapZoneBinaryCallback/*<A, B, R>*/ callback) {
+  if (Zone.current == Zone.ROOT) return callback;
   if (callback == null) return null;
-  return Zone.current.bindUnaryCallback(callback, runGuarded: true);
-}
-
-ZoneBinaryCallback/*<R, A, B>*/ _wrapBinaryZone/*<R, A, B>*/(
-    ZoneBinaryCallback/*<R, A, B>*/ callback) {
-  if (identical(Zone.current, Zone.ROOT)) return callback;
-  if (callback == null) return null;
-  return Zone.current.bindBinaryCallback(callback, runGuarded: true);
+  // We cast to _wrapZoneBinaryCallback/*<A, B, R>*/ to hack around missing
+  // generic method support in zones.
+  // ignore: STRONG_MODE_DOWN_CAST_COMPOSITE
+  _wrapZoneBinaryCallback/*<A, B, R>*/ wrapped =
+      Zone.current.bindBinaryCallback(callback, runGuarded: true);
+  return wrapped;
 }
 
 /**
  * Alias for [querySelector]. Note this function is deprecated because its
  * semantics will be changing in the future.
  */
 @deprecated
 @Experimental()
 Element query(String relativeSelectors) => document.query(relativeSelectors);
 /**
@@ skipping 42 matching lines @@
 ElementList<Element> querySelectorAll(String selectors) => document.querySelectorAll(selectors);
 
 /// A utility for changing the Dart wrapper type for elements.
 abstract class ElementUpgrader {
   /// Upgrade the specified element to be of the Dart type this was created for.
   ///
   /// After upgrading the element passed in is invalid and the returned value
   /// should be used instead.
   Element upgrade(Element element);
 }