DevTools: Get rid of synchronous XHRs in the frontend code

Source/devtools/front_end/profiler/HeapSnapshotProxy.js

Index: Source/devtools/front_end/profiler/HeapSnapshotProxy.js
diff --git a/Source/devtools/front_end/profiler/HeapSnapshotProxy.js b/Source/devtools/front_end/profiler/HeapSnapshotProxy.js
index 5f0324eb7e9091febe46a339f13a2dc9d72f2662..d740895d6892d48f90298decdd022f72e226955d 100644
--- a/Source/devtools/front_end/profiler/HeapSnapshotProxy.js
+++ b/Source/devtools/front_end/profiler/HeapSnapshotProxy.js
@@ -40,12 +40,24 @@ WebInspector.HeapSnapshotWorkerProxy = function(eventHandler)
     this._nextCallId = 1;
     this._callbacks = [];
     this._previousCallbacks = [];
-    this._worker = Runtime.startWorker("heap_snapshot_worker");
-    this._worker.onmessage = this._messageReceived.bind(this);
+    this._pendingWorkerPromise = WorkerRuntime.startWorker("heap_snapshot_worker").then(this._init.bind(this));
 }
 
 WebInspector.HeapSnapshotWorkerProxy.prototype = {
     /**
+     * @param {!Worker} worker
+     */
+    _init: function(worker)
+    {
+        this._worker = worker;
+        if (this._disposed) {
+            this.dispose();
+            return;
+        }
+        this._worker.onmessage = this._messageReceived.bind(this);
+    },
+
+    /**
      * @param {number} profileUid
      * @param {function(!WebInspector.HeapSnapshotProxy)} snapshotReceivedCallback
      * @return {!WebInspector.HeapSnapshotLoaderProxy}
@@ -60,7 +72,9 @@ WebInspector.HeapSnapshotWorkerProxy.prototype = {
 
     dispose: function()
     {
-        this._worker.terminate();
+        this._disposed = true;
+        if (this._worker)
+            this._worker.terminate();
         if (this._interval)
             clearInterval(this._interval);
     },
@@ -171,9 +185,22 @@ WebInspector.HeapSnapshotWorkerProxy.prototype = {
         callback(data.result);
     },
 
+    /**
+     * @param {!Object} message
+     */
     _postMessage: function(message)
     {
-        this._worker.postMessage(message);
+        this._pendingWorkerPromise.then(postMessage.bind(this));
+
+        /**
+         * @this {WebInspector.HeapSnapshotWorkerProxy}
+         */
+        function postMessage()
+        {
+            if (this._disposed)
+                return;
+            this._worker.postMessage(message);
+        }
     },
 
     __proto__: WebInspector.Object.prototype
@@ -445,7 +472,7 @@ WebInspector.HeapSnapshotProxy.prototype = {
     },
 
     /**
-     * @param {!function(!WebInspector.HeapSnapshotCommon.Statistics):void} callback
+     * @param {function(!WebInspector.HeapSnapshotCommon.Statistics):void} callback
      */
     getStatistics: function(callback)
     {