[DevTools] Turn starting tracing into promise.

third_party/WebKit/LayoutTests/http/tests/inspector/timeline-test.js

 function wrapCallFunctionForTimeline(f)
 {
     var script = document.createElement("script");
     script.textContent = "(" + f.toString() + ")()\n//# sourceURL=wrapCallFunctionForTimeline.js";
     document.body.appendChild(script);
 }
 
 var initialize_Timeline = function() {
 
 InspectorTest.preloadPanel("timeline");
@@ skipping 72 matching lines @@
 }
 
 InspectorTest.invokeWithTracing = function(functionName, callback, additionalCategories, enableJSSampling)
 {
     var categories = "-*,disabled-by-default-devtools.timeline*,devtools.timeline," + SDK.TracingModel.TopLevelEventCategory;
     if (additionalCategories)
         categories += "," + additionalCategories;
     var timelinePanel = UI.panels.timeline;
     var timelineController = InspectorTest.timelineController();
     timelinePanel._timelineController = timelineController;
-    timelineController._startRecordingWithCategories(categories, enableJSSampling, tracingStarted);
+    timelineController._startRecordingWithCategories(categories, enableJSSampling).then(tracingStarted);
 
     function tracingStarted()
     {
         InspectorTest.callFunctionInPageAsync(functionName).then(onPageActionsDone);
     }
 
     function onPageActionsDone()
     {
         InspectorTest.runWhenTimelineIsReady(callback);
         timelineController.stopRecording();
@@ skipping 340 matching lines @@
 function waitForFrame()
 {
     var callback;
     var promise = new Promise((fulfill) => callback = fulfill);
     if (window.testRunner)
         testRunner.capturePixelsAsyncThen(() => window.requestAnimationFrame(callback));
     else
         window.requestAnimationFrame(callback);
     return promise;
 }