[DevTools] Persist device mode state.

third_party/WebKit/Source/devtools/front_end/emulation/OverridesSupport.js

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 740 matching lines @@
         var showRulersValue = WebInspector.moduleSetting("showMetricsRulers").get();
         for (var target of WebInspector.targetManager.targets(WebInspector.Target.Type.Page)) {
             var domModel = WebInspector.DOMModel.fromTarget(target);
             if (domModel)
                 domModel.setHighlightSettings(showRulersValue && !this._pageResizerActive(), showRulersValue);
         }
     },
 
     _onMainFrameNavigated: function()
     {
-        this._deviceMetricsChanged(false);
+        if (!Runtime.experiments.isEnabled("deviceMode"))
+            this._deviceMetricsChanged(false);
         this._updateUserAgentWarningMessage("");
         this._updateDeviceMetricsWarningMessage("");
     },
 
     _dispatchWarningChanged: function()
     {
         this.dispatchEventToListeners(WebInspector.OverridesSupport.Events.OverridesWarningUpdated);
     },
 
     /**
@@ skipping 38 matching lines @@
     },
 
     __proto__: WebInspector.Object.prototype
 }
 
 
 /**
  * @type {!WebInspector.OverridesSupport}
  */
 WebInspector.overridesSupport;