fix(WebWorker): Don't send messages when the buffer is empty

Closes #4138

modules/angular2/src/web_workers/shared/generic_message_bus.dart

@@ -46,8 +46,10 @@ abstract class GenericMessageBusSink implements MessageBusSink {
   void attachToZone(NgZone zone) {
     _zone = zone;
     _zone.overrideOnEventDone(() {
-      sendMessages(_messageBuffer);
-      _messageBuffer.clear();
+      if (_messageBuffer.length > 0) {
+        sendMessages(_messageBuffer);
+        _messageBuffer.clear();
+      }
     }, false);
   }
 

modules/angular2/src/web_workers/shared/post_message_bus.ts

@@ -73,9 +73,10 @@ export class PostMessageBusSink implements MessageBusSink {
   }
 
   private _handleOnEventDone() {
-    // TODO: Send all buffered messages in one postMessage call
-    this._sendMessages(this._messageBuffer);
-    this._messageBuffer = [];
+    if (this._messageBuffer.length > 0) {
+      this._sendMessages(this._messageBuffer);
+      this._messageBuffer = [];
+    }
   }
 
   private _sendMessages(messages: Array<Object>) { this._postMessageTarget.postMessage(messages); }

modules/angular2/src/web_workers/worker/application.ts

@@ -32,10 +32,8 @@ export function bootstrapWebWorker(
     componentInjectableProviders: Array<Type | Provider | any[]> = null): Promise<ComponentRef> {
   Parse5DomAdapter.makeCurrent();
   var sink = new PostMessageBusSink({
-    postMessage: (message: any, transferrables?:[ArrayBuffer]) => {
-      console.log("Sending", message);
-      _postMessage(message, transferrables);
-    }
+    postMessage:
+        (message: any, transferrables?:[ArrayBuffer]) => { _postMessage(message, transferrables); }
   });
   var source = new PostMessageBusSource();
   var bus = new PostMessageBus(sink, source);

modules/playground/src/web_workers/images/loader.js

@@ -10,7 +10,6 @@ System.config({
 System.import("playground/src/web_workers/images/background_index")
     .then(
         function(m) {
-          console.log("running main");
           try {
             m.main();
           } catch (e) {

modules/playground/src/web_workers/kitchen_sink/loader.js

@@ -8,7 +8,6 @@ System.config({
 System.import("playground/src/web_workers/kitchen_sink/background_index")
     .then(
         function(m) {
-          console.log("running main");
           try {
             m.main();
           } catch (e) {

modules/playground/src/web_workers/todo/loader.js

@@ -8,7 +8,6 @@ System.config({
 System.import("playground/src/web_workers/todo/background_index")
     .then(
         function(m) {
-          console.log("running main");
           try {
             m.main();
           } catch (e) {