DevTools: switch Timeline frontend into buffered mode and remove the corresponding experiment.

LayoutTests/http/tests/inspector/timeline-xhr-event.html

Index: LayoutTests/http/tests/inspector/timeline-xhr-event.html
diff --git a/LayoutTests/http/tests/inspector/timeline-xhr-event.html b/LayoutTests/http/tests/inspector/timeline-xhr-event.html
index b1fc671658cb9809e1169f2c27fd1deafd361727..bbe498be72ff524c4c1297131df8c5942c2efd8d 100644
--- a/LayoutTests/http/tests/inspector/timeline-xhr-event.html
+++ b/LayoutTests/http/tests/inspector/timeline-xhr-event.html
@@ -5,11 +5,11 @@
 <script src="network-test.js"></script>
 <script>
 
-function performActions()
+function performActions(callback)
 {
     var xhr = new XMLHttpRequest();
     xhr.open("GET", "network/resources/resource.php", true);
-    xhr.onload = function () { };  // This is necessary for XHRLoad event.
+    xhr.onload = callback;  // This is necessary for XHRLoad event.
     xhr.onreadystatechange = function () { };  // This is necessary for XHRReadyStateChange event.
     xhr.send(null);
 }
@@ -19,11 +19,7 @@ function test()
     InspectorTest.resetInspectorResourcesData(step1);
     function step1()
     {
-        InspectorTest.startTimeline(function() {
-            InspectorTest.evaluateInPage("performActions()");
-        });
-
-        InspectorTest.waitForRecordType("XHRLoad", finish);
+        InspectorTest.invokeAsyncWithTimeline("performActions", finish);
 
         function finish()
         {