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

third_party/WebKit/Source/devtools/front_end/sdk/NetworkRequest.js

 /*
  * Copyright (C) 2012 Google 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.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 76 matching lines @@
 
     /** @type {!SecurityAgent.SecurityState} */
     this._securityState = SecurityAgent.SecurityState.Unknown;
     /** @type {?NetworkAgent.SecurityDetails} */
     this._securityDetails = null;
 
     /** @type {string} */
     this.connectionId = "0";
 }
 
+/** @enum {symbol} */
 WebInspector.NetworkRequest.Events = {
-    FinishedLoading: "FinishedLoading",
-    TimingChanged: "TimingChanged",
-    RemoteAddressChanged: "RemoteAddressChanged",
-    RequestHeadersChanged: "RequestHeadersChanged",
-    ResponseHeadersChanged: "ResponseHeadersChanged",
-    WebsocketFrameAdded: "WebsocketFrameAdded",
-    EventSourceMessageAdded: "EventSourceMessageAdded",
+    FinishedLoading: Symbol("FinishedLoading"),
+    TimingChanged: Symbol("TimingChanged"),
+    RemoteAddressChanged: Symbol("RemoteAddressChanged"),
+    RequestHeadersChanged: Symbol("RequestHeadersChanged"),
+    ResponseHeadersChanged: Symbol("ResponseHeadersChanged"),
+    WebsocketFrameAdded: Symbol("WebsocketFrameAdded"),
+    EventSourceMessageAdded: Symbol("EventSourceMessageAdded")
 }
 
 /** @enum {string} */
 WebInspector.NetworkRequest.InitiatorType = {
     Other: "other",
     Parser: "parser",
     Redirect: "redirect",
     Script: "script"
 }
 
@@ skipping 1125 matching lines @@
     /**
      * @return {!WebInspector.NetworkManager}
      */
     networkManager: function()
     {
         return this._networkManager;
     },
 
     __proto__: WebInspector.SDKObject.prototype
 }