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

third_party/WebKit/Source/devtools/front_end/emulation/InspectedPagePlaceholder.js

 // Copyright 2014 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.Widget}
  */
 WebInspector.InspectedPagePlaceholder = function()
 {
     WebInspector.Widget.call(this);
     this.element.classList.add("inspected-page-placeholder");
     WebInspector.zoomManager.addEventListener(WebInspector.ZoomManager.Events.ZoomChanged, this._scheduleUpdate, this);
     this._margins = { top: 0, right: 0, bottom: 0, left: 0 };
     this.restoreMinimumSizeAndMargins();
 };
 
+/** @enum {symbol} */
 WebInspector.InspectedPagePlaceholder.Events = {
-    Update: "Update"
+    Update: Symbol("Update")
 };
 
 WebInspector.InspectedPagePlaceholder.MarginValue = 3;
 
 WebInspector.InspectedPagePlaceholder.prototype = {
     _findMargins: function()
     {
         var margins = { top: 0, right: 0, bottom: 0, left: 0 };
 
         if (this._useMargins) {
@@ skipping 63 matching lines @@
     update: function()
     {
         delete this._updateId;
         var rect = this._dipPageRect();
         var bounds = { x: Math.round(rect.x), y: Math.round(rect.y), height: Math.max(1, Math.round(rect.height)), width: Math.max(1, Math.round(rect.width)) };
         this.dispatchEventToListeners(WebInspector.InspectedPagePlaceholder.Events.Update, bounds);
     },
 
     __proto__: WebInspector.Widget.prototype
 };