Only use special method to send messages to helper isolate.

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 9f92c2b4517c6fee2bc2dfd6a5166504c06f2bc3..8623dd8ec9e177e070f0e028f83210da909beb6d 100644
--- a/sdk/lib/html/dartium/html_dartium.dart
+++ b/sdk/lib/html/dartium/html_dartium.dart
@@ -35053,7 +35053,6 @@ class Rect {
 // BSD-style license that can be found in the LICENSE file.
 
 
-// TODO(antonm): support not DOM isolates too.
 class _Timer implements Timer {
   final canceller;
 
@@ -35104,22 +35103,8 @@ 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);
   }
 }
 
@@ -36349,9 +36334,29 @@ class _DOMStringMap extends NativeFieldWrapperClass1 implements Map<String, Stri
   bool get isEmpty => Maps.isEmpty(this);
 }
 
-final Future<SendPort> _HELPER_ISOLATE_PORT =
+final Future<SendPort> __HELPER_ISOLATE_PORT =
     spawnDomFunction(_helperIsolateMain);
 
+// 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.
+SendPort __SEND_PORT;
+
+_sendToHelperIsolate(msg, SendPort replyTo) {
+  if (__SEND_PORT != null) {
+    __SEND_PORT.send(msg, replyTo);
+  } else {
+    __HELPER_ISOLATE_PORT.then((port) {
+      __SEND_PORT = port;
+      __SEND_PORT.send(msg, replyTo);
+    });
+  }
+}
+
 final _TIMER_REGISTRY = new Map<SendPort, Timer>();
 
 const _NEW_TIMER = 'NEW_TIMER';
@@ -36381,9 +36386,7 @@ _helperIsolateMain() {
 
 final _printClosure = window.console.log;
 final _pureIsolatePrintClosure = (s) {
-  _HELPER_ISOLATE_PORT.then((sendPort) {
-    sendPort.send([_PRINT, s]);
-  });
+  _sendToHelperIsolate([_PRINT, s]);
 };
 
 final _forwardingPrintClosure = _Utils.forwardingPrint;