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

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

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 2012 Intel 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.
@@ skipping 1753 matching lines @@
 WebInspector.TimelineCategory = function(name, title, visible, childColor, color)
 {
     this.name = name;
     this.title = title;
     this.visible = visible;
     this.childColor = childColor;
     this.color = color;
     this.hidden = false;
 }
 
+/** @enum {symbol} */
 WebInspector.TimelineCategory.Events = {
-    VisibilityChanged: "VisibilityChanged"
+    VisibilityChanged: Symbol("VisibilityChanged")
 };
 
 WebInspector.TimelineCategory.prototype = {
     /**
      * @return {boolean}
      */
     get hidden()
     {
         return this._hidden;
     },
@@ skipping 360 matching lines @@
     case warnings.V8Deopt:
         span.appendChild(WebInspector.linkifyURLAsNode("https://github.com/GoogleChrome/devtools-docs/issues/53",
             WebInspector.UIString("Not optimized"), undefined, true));
         span.createTextChild(WebInspector.UIString(": %s", eventData["deoptReason"]));
         break;
     default:
         console.assert(false, "Unhandled TimelineModel.WarningType");
     }
     return span;
 }