[DevTools] Auto-attach to cross-process subframes under 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 63 matching lines @@
             new WebInspector.VersionController().updateVersion();
     },
 
     /**
      * @param {!Object<string, string>} prefs
      */
     _initializeExperiments: function(prefs)
     {
         Runtime.experiments.register("accessibilityInspection", "Accessibility Inspection");
         Runtime.experiments.register("applyCustomStylesheet", "Allow custom UI themes");
+        Runtime.experiments.register("autoAttachToCrossProcessSubframes", "Auto-attach to cross-process subframes", true);
         Runtime.experiments.register("blackboxJSFramesOnTimeline", "Blackbox JavaScript frames on Timeline", true);
         Runtime.experiments.register("colorContrastRatio", "Contrast ratio line in color picker", true);
         Runtime.experiments.register("continueToFirstInvocation", "Continue to first invocation", true);
         Runtime.experiments.register("emptySourceMapAutoStepping", "Empty sourcemap auto-stepping");
         Runtime.experiments.register("inputEventsOnTimelineOverview", "Input events on Timeline overview", true);
         Runtime.experiments.register("layersPanel", "Layers panel");
         Runtime.experiments.register("layoutEditor", "Layout editor", true);
         Runtime.experiments.register("inspectTooltip", "Dark inspect element tooltip");
         Runtime.experiments.register("liveSASS", "Live SASS");
         Runtime.experiments.register("nodeDebugging", "Node debugging", true);
@@ skipping 1013 matching lines @@
      * @override
      * @return {?Element}
      */
     settingElement: function()
     {
         return WebInspector.SettingsUI.createSettingCheckbox(WebInspector.UIString("Show rulers"), WebInspector.moduleSetting("showMetricsRulers"));
     }
 }
 
 new WebInspector.Main();