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

third_party/WebKit/Source/devtools/front_end/host/InspectorFrontendHostAPI.js

 // Copyright (c) 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.
 
 
 /** @interface */
 function InspectorFrontendHostAPI()
 {
 }
 window.InspectorFrontendHostAPI = InspectorFrontendHostAPI;
 /** @typedef
 {{
     type: string,
     id: (number|undefined),
     label: (string|undefined),
     enabled: (boolean|undefined),
     checked: (boolean|undefined),
     subItems: (!Array.<!InspectorFrontendHostAPI.ContextMenuDescriptor>|undefined)
 }} */
 InspectorFrontendHostAPI.ContextMenuDescriptor;
 
 /** @typedef
 {{
     statusCode: number,
     headers: (!Object.<string, string>|undefined)
 }} */
 InspectorFrontendHostAPI.LoadNetworkResourceResult;
 
+/** @enum {string} */
 InspectorFrontendHostAPI.Events = {
     AddExtensions: "addExtensions",
     AppendedToURL: "appendedToURL",
     CanceledSaveURL: "canceledSaveURL",
     ContextMenuCleared: "contextMenuCleared",
     ContextMenuItemSelected: "contextMenuItemSelected",
     DeviceCountUpdated: "deviceCountUpdated",
     DevicesDiscoveryConfigChanged: "devicesDiscoveryConfigChanged",
     DevicesPortForwardingStatusChanged: "devicesPortForwardingStatusChanged",
     DevicesUpdated: "devicesUpdated",
@@ skipping 249 matching lines @@
      */
     isUnderTest: function() { },
 
     readyForTest: function() { },
 
     /**
      * @return {boolean}
      */
     isHostedMode: function() { }
 }