DevTools: Use JS symbols instead of strings for eligible events.

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

 /*
  * Copyright (C) 2013 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 29 matching lines @@
     this.element.classList.add("layer-details-view");
     this._layerViewHost = layerViewHost;
     this._layerViewHost.registerView(this);
     this._emptyWidget = new WebInspector.EmptyWidget(WebInspector.UIString("Select a layer to see its details"));
     this._buildContent();
 }
 
 /**
  * @enum {string}
  */
+/** @enum {symbol} */
 WebInspector.LayerDetailsView.Events = {
-    PaintProfilerRequested: "PaintProfilerRequested"
+    PaintProfilerRequested: Symbol("PaintProfilerRequested")
 }
 
 /**
  * @type {!Object.<string, string>}
  */
 WebInspector.LayerDetailsView.CompositingReasonDetail = {
     "transform3D": WebInspector.UIString("Composition due to association with an element with a CSS 3D transform."),
     "video": WebInspector.UIString("Composition due to association with a <video> element."),
     "canvas": WebInspector.UIString("Composition due to the element being a <canvas> element."),
     "plugin": WebInspector.UIString("Composition due to association with a plugin."),
@@ skipping 154 matching lines @@
             var text = WebInspector.LayerDetailsView.CompositingReasonDetail[compositingReasons[i]] || compositingReasons[i];
             // If the text is more than one word but does not terminate with period, add the period.
             if (/\s.*[^.]$/.test(text))
                 text += ".";
             list.createChild("li").textContent = text;
         }
     },
 
     __proto__: WebInspector.Widget.prototype
 }