Reduce footprint of HTML Timer by not creating a "cancel" closure.

tools/dom/src/native_DOMImplementation.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 html;
 
 class _ConsoleVariables {
   Map<String, Object> _data = new Map<String, Object>();
 
   /**
@@ skipping 512 matching lines @@
 
 final _forwardingPrintClosure = _Utils.forwardingPrint;
 
 final _uriBaseClosure = () => Uri.parse(window.location.href);
 
 final _pureIsolateUriBaseClosure = () {
   throw new UnimplementedError("Uri.base on a background isolate "
                                "is not supported in the browser");
 };
 
- class _Timer implements Timer {
-  var _canceler;
+class _Timer implements Timer {
+  const int _STATE_TIMEOUT = 0;
+  const int _STATE_INTERVAL = 1;
+  var _state;
 
   _Timer(int milliSeconds, void callback(Timer timer), bool repeating) {
-
     if (repeating) {
-      int id = window._setInterval(() {
+      _state = window._setInterval(() {
         callback(this);
-      }, milliSeconds);
-      _canceler = () => window._clearInterval(id);
+      }, milliSeconds) * 2 + _STATE_INTERVAL;
     } else {
-      int id = window._setTimeout(() {
-        _canceler = null;
+      _state = window._setTimeout(() {
+        _state = null;
         callback(this);
-      }, milliSeconds);
-      _canceler = () => window._clearTimeout(id);
+      }, milliSeconds) * 2 + _STATE_TIMEOUT;
     }
   }
 
   void cancel() {
-    if (_canceler != null) {
-      _canceler();
+    if (_state == null) return;
+    int id = _state ~/ 2;
+    if ((_state & 1) == _STATE_TIMEOUT) {
+      window._clearTimeout(id);
+    } else {
+      window._clearInterval(id);
     }
-    _canceler = null;
+    _state = null;
   }
 
-  bool get isActive => _canceler != null;
+  bool get isActive => _state != null;
 }
 
 get _timerFactoryClosure =>
     (int milliSeconds, void callback(Timer timer), bool repeating) {
   return new _Timer(milliSeconds, callback, repeating);
 };
 
 get _pureIsolateTimerFactoryClosure =>
     ((int milliSeconds, void callback(Timer time), bool repeating) =>
   throw new UnimplementedError("Timers on background isolates "
@@ skipping 39 matching lines @@
   _scheduleImmediateHelper._schedule(callback);
 };
 
 get _pureIsolateScheduleImmediateClosure => ((void callback()) =>
   throw new UnimplementedError("scheduleMicrotask in background isolates "
                                "are not supported in the browser"));
 
 void _initializeCustomElement(Element e) {
   _Utils.initializeCustomElement(e);
 }