Revert "Remove _WorkerStub hack to make benefit closing an isolate."

dart/sdk/lib/_internal/compiler/implementation/lib/isolate_helper.dart

Index: dart/sdk/lib/_internal/compiler/implementation/lib/isolate_helper.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/lib/isolate_helper.dart b/dart/sdk/lib/_internal/compiler/implementation/lib/isolate_helper.dart
index fa07503471509ca1d46042ddefa71ade3556e4a5..ebbb9fd02a566663cd58f7f630b8ba1387d653ff 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/lib/isolate_helper.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/lib/isolate_helper.dart
@@ -412,6 +412,21 @@ class _MainManagerStub implements _ManagerStub {
   void terminate() {}  // Nothing useful to do here.
 }
 
+/**
+ * A stub for interacting with a manager built on a web worker. This
+ * definition uses a 'hidden' type (* prefix on the native name) to
+ * enforce that the type is defined dynamically only when web workers
+ * are actually available.
+ */
+// @Native("*Worker");
+class _WorkerStub implements _ManagerStub {
+  get id => JS("", "#.id", this);
+  void set id(i) { JS("void", "#.id = #", this, i); }
+  void set onmessage(f) { JS("void", "#.onmessage = #", this, f); }
+  void postMessage(msg) { JS("void", "#.postMessage(#)", this, msg); }
+  void terminate() { JS("void", "#.terminate()", this); }
+}
+
 const String _SPAWNED_SIGNAL = "spawned";
 
 var globalThis = IsolateNatives.computeGlobalThis();
@@ -473,6 +488,9 @@ class IsolateNatives {
 
   static computeGlobalThis() => JS('', 'function() { return this; }()');
 
+  /** Starts a new worker with the given URL. */
+  static _WorkerStub _newWorker(url) => JS("_WorkerStub", r"new Worker(#)", url);
+
   /**
    * Assume that [e] is a browser message event and extract its message data.
    * We don't import the dom explicitly so, when workers are disabled, this
@@ -520,8 +538,8 @@ class IsolateNatives {
         break;
       case 'close':
         _log("Closing Worker");
-        _globalState.managers.remove(getId(sender));
-        doTerminate(sender);
+        _globalState.managers.remove(sender.id);
+        sender.terminate();
         _globalState.topEventLoop.run();
         break;
       case 'log':
@@ -540,22 +558,6 @@ class IsolateNatives {
     }
   }
 
-
-  static getId(/* Worker or _ManagerStub */ worker) {
-    if (worker is _ManagerStub) return worker.id;
-    return JS('', '#.id', worker);
-  }
-
-  static doTerminate(/* Worker or _ManagerStub */ worker) {
-    if (worker is _ManagerStub) return worker.terminate();
-    return JS('', '#.terminate()', worker);
-  }
-
-  static doPostMessage(/* Worker or _ManagerStub */ worker, message) {
-    if (worker is _ManagerStub) return worker.postMessage(message);
-    return JS('', '#.postMessage(#)', worker, message);
-  }
-
   /** Log a message, forwarding to the main [_Manager] if appropriate. */
   static _log(msg) {
     if (_globalState.isWorker) {
@@ -673,26 +675,24 @@ class IsolateNatives {
    */
   static void _spawnWorker(functionName, uri, replyPort) {
     if (uri == null) uri = thisScript;
-    final worker = JS('var', 'new Worker(#)', uri);
-
-    var processWorkerMessageTrampoline =
-      JS('', 'function(e) { #(#, e); }',
-         DART_CLOSURE_TO_JS(_processWorkerMessage),
-         worker);
-    JS('void', '#.onmessage = #', worker, processWorkerMessageTrampoline);
+    final worker = _newWorker(uri);
+    worker.onmessage = JS('',
+                          'function(e) { #(#, e); }',
+                          DART_CLOSURE_TO_JS(_processWorkerMessage),
+                          worker);
     var workerId = _globalState.nextManagerId++;
     // We also store the id on the worker itself so that we can unregister it.
-    JS('void', '#.id = #', worker, workerId);
+    worker.id = workerId;
     _globalState.managers[workerId] = worker;
-    JS('void', '#.postMessage(#)', worker, _serializeMessage({
-        'command': 'start',
-        'id': workerId,
-        // Note: we serialize replyPort twice because the child worker needs to
-        // first deserialize the worker id, before it can correctly deserialize
-        // the port (port deserialization is sensitive to what is the current
-        // workerId).
-        'replyTo': _serializeMessage(replyPort),
-        'functionName': functionName }));
+    worker.postMessage(_serializeMessage({
+      'command': 'start',
+      'id': workerId,
+      // Note: we serialize replyPort twice because the child worker needs to
+      // first deserialize the worker id, before it can correctly deserialize
+      // the port (port deserialization is sensitive to what is the current
+      // workerId).
+      'replyTo': _serializeMessage(replyPort),
+      'functionName': functionName }));
   }
 }
 
@@ -809,7 +809,7 @@ class _WorkerSendPort extends _BaseSendPort implements SendPort {
         // Deliver the message only if the worker is still alive.
         _ManagerStub manager = _globalState.managers[_workerId];
         if (manager != null) {
-          IsolateNatives.doPostMessage(manager, workerMessage);
+          manager.postMessage(workerMessage);
         }
       }
     });