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

third_party/WebKit/Source/devtools/front_end/extensions/ExtensionAPI.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 31 matching lines @@
 
     if (!apiPrivate.panels)
         apiPrivate.panels = {};
     apiPrivate.panels.SearchAction = {
         CancelSearch: "cancelSearch",
         PerformSearch: "performSearch",
         NextSearchResult: "nextSearchResult",
         PreviousSearchResult: "previousSearchResult"
     };
 
+    /** @enum {string} */
     apiPrivate.Events = {
         AuditStarted: "audit-started-",
         ButtonClicked: "button-clicked-",
         PanelObjectSelected: "panel-objectSelected-",
         NetworkRequestFinished: "network-request-finished",
         OpenResource: "open-resource",
         PanelSearch: "panel-search-",
         ResourceAdded: "resource-added",
         ResourceContentCommitted: "resource-content-committed",
         ViewShown: "view-shown-",
         ViewHidden: "view-hidden-"
     };
 
+    /** @enum {string} */
     apiPrivate.Commands = {
         AddAuditCategory: "addAuditCategory",
         AddAuditResult: "addAuditResult",
         AddRequestHeaders: "addRequestHeaders",
         ApplyStyleSheet: "applyStyleSheet",
         CreatePanel: "createPanel",
         CreateSidebarPane: "createSidebarPane",
         CreateToolbarButton: "createToolbarButton",
         EvaluateOnInspectedPage: "evaluateOnInspectedPage",
         ForwardKeyboardEvent: "_forwardKeyboardEvent",
@@ skipping 936 matching lines @@
 {
     return "(function(injectedScriptId){ " +
         "var extensionServer;" +
         defineCommonExtensionSymbols.toString() + ";" +
         injectedExtensionAPI.toString() + ";" +
         buildPlatformExtensionAPI(extensionInfo, inspectedTabId, themeName) + ";" +
         "platformExtensionAPI(injectedExtensionAPI(injectedScriptId));" +
         "return {};" +
         "})";
 }