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

third_party/WebKit/Source/devtools/front_end/elements/ElementsTreeOutline.js

 /*
  * Copyright (C) 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2008 Matt Lilek <webkit@mattlilek.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 83 matching lines @@
  * @return {?WebInspector.ElementsTreeOutline}
  */
 WebInspector.ElementsTreeOutline.forDOMModel = function(domModel)
 {
     return domModel[WebInspector.ElementsTreeOutline._treeOutlineSymbol] || null;
 }
 
 /** @typedef {{node: !WebInspector.DOMNode, isCut: boolean}} */
 WebInspector.ElementsTreeOutline.ClipboardData;
 
-/**
- * @enum {string}
- */
+/** @enum {symbol} */
 WebInspector.ElementsTreeOutline.Events = {
-    SelectedNodeChanged: "SelectedNodeChanged",
-    ElementsTreeUpdated: "ElementsTreeUpdated"
+    SelectedNodeChanged: Symbol("SelectedNodeChanged"),
+    ElementsTreeUpdated: Symbol("ElementsTreeUpdated")
 }
 
 /**
  * @const
  * @type {!Object.<string, string>}
  */
 WebInspector.ElementsTreeOutline.MappedCharToEntity = {
     "\u00a0": "nbsp",
     "\u0093": "#147", // <control>
     "\u00ad": "shy",
@@ skipping 1679 matching lines @@
             if (node) {
                 this.treeOutline._selectedDOMNode = node;
                 this.treeOutline._selectedNodeChanged();
             }
         }
         return true;
     },
 
     __proto__: TreeElement.prototype
 }