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

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

 /*
  * Copyright (C) 2012 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 1866 matching lines @@
     WebInspector.Object.call(this);
 
     this._categoryFilter = new WebInspector.TimelineCategoryFilter();
     this._durationFilter = new WebInspector.TimelineIsLongFilter();
     this._textFilter = new WebInspector.TimelineTextFilter();
     this._filters = [this._categoryFilter, this._durationFilter, this._textFilter];
 
     this._createFilterBar();
 }
 
+/** @enum {symbol} */
 WebInspector.TimelineFilters.Events = {
     FilterChanged: Symbol("FilterChanged")
 };
 
 WebInspector.TimelineFilters._durationFilterPresetsMs = [0, 1, 15];
 
 WebInspector.TimelineFilters.prototype = {
     /**
      * @return {!Array<!WebInspector.TimelineModel.Filter>}
      */
@@ skipping 222 matching lines @@
     _onKeyDown: function(event)
     {
         if (event.keyCode === WebInspector.KeyboardShortcut.Keys.Enter.code) {
             event.preventDefault();
             this._apply();
         }
     },
 
     __proto__: WebInspector.HBox.prototype
 }