DevTools: introduce "Track CSS Usage" experiment

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

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 /**
  * @implements {WebInspector.TargetManager.Observer}
  * @implements {WebInspector.TracingManagerClient}
  * @unrestricted
  */
 WebInspector.TimelineController = class {
   /**
    * @param {!WebInspector.Target} target
    * @param {!WebInspector.TimelineLifecycleDelegate} delegate
    * @param {!WebInspector.TracingModel} tracingModel
    */
   constructor(target, delegate, tracingModel) {
     this._delegate = delegate;
     this._target = target;
     this._tracingModel = tracingModel;
     this._targets = [];
     WebInspector.targetManager.observeTargets(this);
+
+    if (Runtime.experiments.isEnabled('timelineRuleUsageRecording')) {

[alph, 2016/11/08 17:10:25]

no need for {}

+      this._markUnusedCSS = WebInspector.settings.createSetting('timelineMarkUnusedCSS', false);
+    }
   }
 
   /**
    * @param {boolean} captureCauses
    * @param {boolean} enableJSSampling
    * @param {boolean} captureMemory
    * @param {boolean} capturePictures
    * @param {boolean} captureFilmStrip
    */
   startRecording(captureCauses, enableJSSampling, captureMemory, capturePictures, captureFilmStrip) {
@@ skipping 36 matching lines @@
 
     var categories = categoriesArray.join(',');
     this._startRecordingWithCategories(categories, enableJSSampling);
   }
 
   stopRecording() {
     var tracingStoppedPromises = [];
     tracingStoppedPromises.push(new Promise(resolve => this._tracingCompleteCallback = resolve));
     tracingStoppedPromises.push(this._stopProfilingOnAllTargets());
     this._target.tracingManager.stop();
-    tracingStoppedPromises.push(WebInspector.targetManager.resumeAllTargets());
+
+    if (!Runtime.experiments.isEnabled('timelineRuleUsageRecording') || !this._markUnusedCSS.get())

[alph, 2016/11/08 17:10:25]

if an experiment is enabled after opening timeline, this._markUnusedCSS will be
undefined.

+      tracingStoppedPromises.push(WebInspector.targetManager.resumeAllTargets());
+
     Promise.all(tracingStoppedPromises).then(() => this._allSourcesFinished());
 
     this._delegate.loadingStarted();
 
     for (var traceProvider of this._extensionTraceProviders)
       traceProvider.stop();
   }
 
   /**
    * @override
@@ skipping 65 matching lines @@
     this._profiling = false;
     return Promise.all(targets.map(this._stopProfilingOnTarget, this));
   }
 
   /**
    * @param {string} categories
    * @param {boolean=} enableJSSampling
    * @param {function(?string)=} callback
    */
   _startRecordingWithCategories(categories, enableJSSampling, callback) {
-    WebInspector.targetManager.suspendAllTargets();
+
+    if (!Runtime.experiments.isEnabled('timelineRuleUsageRecording') || !this._markUnusedCSS.get())

[alph, 2016/11/08 17:10:25]

This looks bad. We want to suspend targets not involved in timeline recording.

+      WebInspector.targetManager.suspendAllTargets();
+
     var profilingStartedPromise = enableJSSampling && !Runtime.experiments.isEnabled('timelineTracingJSProfile') ?
         this._startProfilingOnAllTargets() :
         Promise.resolve();
     var samplingFrequencyHz = WebInspector.moduleSetting('highResolutionCpuProfiling').get() ? 10000 : 1000;
     var options = 'sampling-frequency=' + samplingFrequencyHz;
     var target = this._target;
     var tracingManager = target.tracingManager;
     WebInspector.targetManager.suspendReload(target);
     profilingStartedPromise.then(tracingManager.start.bind(tracingManager, this, categories, options, onTraceStarted));
     /**
@@ skipping 92 matching lines @@
   }
 
   /**
    * @param {number} progress
    * @override
    */
   eventsRetrievalProgress(progress) {
     this._delegate.loadingProgress(progress);
   }
 };