DevTools: introduce "Track CSS Usage" experiment

third_party/WebKit/Source/devtools/front_end/main/Main.js

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2007 Matt Lilek (pewtermoose@gmail.com).
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
@@ skipping 108 matching lines @@
     Runtime.experiments.register('timelineShowAllEvents', 'Show all events on Timeline', true);
     Runtime.experiments.register('timelineShowAllProcesses', 'Show all processes on Timeline', true);
     Runtime.experiments.register('securityPanel', 'Security panel');
     Runtime.experiments.register('sourceDiff', 'Source diff');
     Runtime.experiments.register('terminalInDrawer', 'Terminal in drawer', true);
     Runtime.experiments.register('timelineFlowEvents', 'Timeline flow events', true);
     Runtime.experiments.register('timelineInvalidationTracking', 'Timeline invalidation tracking', true);
     Runtime.experiments.register('timelineRecordingPerspectives', 'Timeline recording perspectives UI');
     Runtime.experiments.register('timelineTracingJSProfile', 'Timeline tracing based JS profiler', true);
     Runtime.experiments.register('timelineV8RuntimeCallStats', 'V8 Runtime Call Stats on Timeline', true);
+    Runtime.experiments.register('timelineRuleUsageRecording', 'Timeline tracing the CSS rule usage');

[caseq, 2016/11/04 21:10:02]

Track CSS rules usage while recording Timeline.

 
     Runtime.experiments.cleanUpStaleExperiments();
 
     if (InspectorFrontendHost.isUnderTest()) {
       var testPath = JSON.parse(prefs['testPath'] || '""');
       // Enable experiments for testing.
       if (testPath.indexOf('layers/') !== -1)
         Runtime.experiments.enableForTest('layersPanel');
       if (testPath.indexOf('timeline/') !== -1 || testPath.indexOf('layers/') !== -1)
         Runtime.experiments.enableForTest('layersPanel');
@@ skipping 920 matching lines @@
    * @override
    * @return {?Element}
    */
   settingElement() {
     return WebInspector.SettingsUI.createSettingCheckbox(
         WebInspector.UIString('Show rulers'), WebInspector.moduleSetting('showMetricsRulers'));
   }
 };
 
 new WebInspector.Main();
+

[caseq, 2016/11/04 21:10:02]

revert this line.