Add isActive field on Timer.

sdk/lib/html/dartium/html_dartium.dart

Index: sdk/lib/html/dartium/html_dartium.dart
diff --git a/sdk/lib/html/dartium/html_dartium.dart b/sdk/lib/html/dartium/html_dartium.dart
index 81f000f1ece763388a2bd7f83b60f49339edfd7d..132b803a12982695b47422f4774478d60ec13e6f 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -31021,29 +31021,43 @@ final _forwardingPrintClosure = _Utils.forwardingPrint;
 
 class _Timer implements Timer {
   final canceller;
+  bool _isDone = false;
 
   _Timer(this.canceller);
 
-  void cancel() { canceller(); }
-}
+  factory _Timer.timerFactoryClosure(int milliSeconds,
+                                     void callback(Timer timer),
+                                     bool repeating) {
+    var maker;
+    var canceller;
+    if (repeating) {
+      maker = window._setInterval;
+      canceller = window._clearInterval;
+    } else {
+      maker = window._setTimeout;
+      canceller = window._clearTimeout;
+    }
+    Timer timer;
+    final int id = maker(() { _isDone = true; callback(timer);}, milliSeconds);
+    timer = new _Timer(() { canceller(id); });
+    return timer;
+  }
 
-get _timerFactoryClosure => (int milliSeconds, void callback(Timer timer), bool repeating) {
-  var maker;
-  var canceller;
-  if (repeating) {
-    maker = window._setInterval;
-    canceller = window._clearInterval;
-  } else {
-    maker = window._setTimeout;
-    canceller = window._clearTimeout;
+  void cancel() {
+    _isDone = true;
+    canceller();
   }
-  Timer timer;
-  final int id = maker(() { callback(timer); }, milliSeconds);
-  timer = new _Timer(() { canceller(id); });
-  return timer;
+
+  bool get isActive => !_isDone;
+}
+
+get _timerFactoryClosure =>
+    (int milliSeconds, void callback(Timer timer), bool repeating) {
+  return _Timer.timerFactoryClosure(milliseconds, callback, repeating);
 };
 
 class _PureIsolateTimer implements Timer {
+  bool _isDone = false;
   final ReceivePort _port = new ReceivePort();
   SendPort _sendPort; // Effectively final.
 
@@ -31053,6 +31067,7 @@ class _PureIsolateTimer implements Timer {
     _sendPort = _port.toSendPort();
     _port.receive((msg, replyTo) {
       assert(msg == _TIMER_PING);
+      _isDone = !repeating;
       callback(this);
       if (!repeating) _cancel();
     });
@@ -31066,12 +31081,15 @@ class _PureIsolateTimer implements Timer {
   }
 
   void _cancel() {
+    _isDone = true;
     _port.close();
   }
 
   _send(msg) {
     _sendToHelperIsolate(msg, _sendPort);
   }
+
+  bool get isActive => !_isDone;
 }
 
 get _pureIsolateTimerFactoryClosure =>