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

third_party/WebKit/Source/devtools/front_end/sdk/RuntimeModel.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 33 matching lines @@
     /** @type {!Map<number, !WebInspector.ExecutionContext>} */
     this._executionContextById = new Map();
     this._executionContextComparator = WebInspector.ExecutionContext.comparator;
 
     if (WebInspector.moduleSetting("customFormatters").get())
         this._agent.setCustomObjectFormatterEnabled(true);
 
     WebInspector.moduleSetting("customFormatters").addChangeListener(this._customFormattersStateChanged.bind(this));
 }
 
+/** @enum {symbol} */
 WebInspector.RuntimeModel.Events = {
-    ExecutionContextCreated: "ExecutionContextCreated",
-    ExecutionContextDestroyed: "ExecutionContextDestroyed",
-    ExecutionContextChanged: "ExecutionContextChanged",
-    ExecutionContextOrderChanged: "ExecutionContextOrderChanged"
+    ExecutionContextCreated: ("ExecutionContextCreated"),
+    ExecutionContextDestroyed: ("ExecutionContextDestroyed"),
+    ExecutionContextChanged: ("ExecutionContextChanged"),
+    ExecutionContextOrderChanged: ("ExecutionContextOrderChanged")
 }
 
 WebInspector.RuntimeModel._privateScript = "private script";
 
 WebInspector.RuntimeModel.prototype = {
 
     /**
      * @return {!Array.<!WebInspector.ExecutionContext>}
      */
     executionContexts: function()
@@ skipping 942 matching lines @@
     /**
      * @return {boolean}
      */
     isNormalListenerType: function()
     {
         return this._listenerType === "normal";
     },
 
     __proto__: WebInspector.SDKObject.prototype
 }