Only use special method to send messages to helper isolate.

tools/dom/src/Timer.dart

Index: tools/dom/src/Timer.dart
diff --git a/tools/dom/src/Timer.dart b/tools/dom/src/Timer.dart
index 8d3660976a89b6319a3c335345ed5dac3014f78f..604899bc47759e7076c04959f63cbe451e6a8352 100644
--- a/tools/dom/src/Timer.dart
+++ b/tools/dom/src/Timer.dart
@@ -4,7 +4,6 @@
 
 part of html;
 
-// TODO(antonm): support not DOM isolates too.
 class _Timer implements Timer {
   final canceller;
 
@@ -55,22 +54,8 @@ class _PureIsolateTimer implements Timer {
     _port.close();
   }
 
-  // Tricky part.
-  // Once _HELPER_ISOLATE_PORT gets resolved, it will still delay in .then
-  // and to delay Timer.run is used. However, Timer.run will try to register
-  // another Timer and here we got stuck: event cannot be posted as then
-  // callback is not executed because it's delayed with timer.
-  // Therefore once future is resolved, it's unsafe to call .then on it
-  // in Timer code.
   _send(msg) {
-    if (_SEND_PORT != null) {
-      _SEND_PORT.send(msg, _sendPort);
-    } else {
-      _HELPER_ISOLATE_PORT.then((port) {
-        _SEND_PORT = port;
-        _SEND_PORT.send(msg, _sendPort);
-      });
-    }
+    _sendToHelperIsolate(msg, _sendPort);
   }
 }