[DevTools] Turn starting tracing into promise.

third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js

Index: third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js
diff --git a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js
index 00272073b3724b5e22dd9482964aa1fe6f578aa6..f66e86d5429a2dfd34769b63a7bd60ba18f62dbd 100644
--- a/third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js
+++ b/third_party/WebKit/Source/devtools/front_end/timeline/TimelineController.js
@@ -33,6 +33,7 @@ Timeline.TimelineController = class {
   /**
    * @param {!Timeline.TimelineController.RecordingOptions} options
    * @param {!Array<!Extensions.ExtensionTraceProvider>} providers
+   * @return {!Promise}
    */
   startRecording(options, providers) {
     this._extensionTraceProviders = Extensions.extensionServer.traceProviders().slice();
@@ -72,8 +73,9 @@ Timeline.TimelineController = class {
     this._extensionSessions =
         providers.map(provider => new Timeline.ExtensionTracingSession(provider, this._performanceModel));
     this._extensionSessions.forEach(session => session.start());
-    this._startRecordingWithCategories(categoriesArray.join(','), options.enableJSSampling);
+    var startPromise = this._startRecordingWithCategories(categoriesArray.join(','), options.enableJSSampling);
     this._performanceModel.setRecordStartTime(Date.now());
+    return startPromise;
   }
 
   stopRecording() {
@@ -169,27 +171,18 @@ Timeline.TimelineController = class {
   /**
    * @param {string} categories
    * @param {boolean=} enableJSSampling
-   * @param {function(?string)=} callback
+   * @return {!Promise}
    */
-  _startRecordingWithCategories(categories, enableJSSampling, callback) {
+  _startRecordingWithCategories(categories, enableJSSampling) {
     SDK.targetManager.suspendAllTargets();
     var profilingStartedPromise = enableJSSampling && !Runtime.experiments.isEnabled('timelineTracingJSProfile') ?
         this._startProfilingOnAllTargets() :
         Promise.resolve();
     var samplingFrequencyHz = Common.moduleSetting('highResolutionCpuProfiling').get() ? 10000 : 1000;
     var options = 'sampling-frequency=' + samplingFrequencyHz;
-    var target = this._target;
-    var tracingManager = target.tracingManager;
-    SDK.targetManager.suspendReload(target);
-    profilingStartedPromise.then(tracingManager.start.bind(tracingManager, this, categories, options, onTraceStarted));
-    /**
-     * @param {?string} error
-     */
-    function onTraceStarted(error) {
-      SDK.targetManager.resumeReload(target);
-      if (callback)
-        callback(error);
-    }
+    var tracingManager = this._target.tracingManager;
+    return profilingStartedPromise.then(
+        tracingManager.start.bind(tracingManager, this, categories, options, undefined));

[caseq, 2017/02/27 23:13:38]

Looks like we need to defer this to when tracingManager.start() asynchronously
completes.

[dgozman, 2017/02/28 01:58:17]

Good catch! Done.

   }
 
   /**