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

third_party/WebKit/Source/devtools/front_end/components_lazy/FilmStripView.js

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 /**
  * @constructor
  * @extends {WebInspector.HBox}
  */
 WebInspector.FilmStripView = function()
 {
     WebInspector.HBox.call(this, true);
     this.registerRequiredCSS("components_lazy/filmStripView.css");
     this.contentElement.classList.add("film-strip-view");
     this._statusLabel = this.contentElement.createChild("div", "label");
     this.reset();
     this.setMode(WebInspector.FilmStripView.Modes.TimeBased);
 }
 
+/** @enum {symbol} */
 WebInspector.FilmStripView.Events = {
-    FrameSelected: "FrameSelected",
-    FrameEnter: "FrameEnter",
-    FrameExit: "FrameExit",
+    FrameSelected: Symbol("FrameSelected"),
+    FrameEnter: Symbol("FrameEnter"),
+    FrameExit: Symbol("FrameExit"),
 }
 
 WebInspector.FilmStripView.Modes = {
     TimeBased: "TimeBased",
     FrameBased: "FrameBased"
 }
 
 WebInspector.FilmStripView.prototype = {
     /**
      * @param {string} mode
@@ skipping 287 matching lines @@
      */
     _render: function()
     {
         var frame = this._frames[this._index];
         this._timeLabel.textContent = Number.millisToString(frame.timestamp - this._zeroTime);
         return frame.imageDataPromise().then(WebInspector.FilmStripView._setImageData.bind(null, this._imageElement)).then(this._resize.bind(this));
     },
 
     __proto__: WebInspector.VBox.prototype
 }