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

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

 /**
  * @constructor
  * @extends {WebInspector.SDKModel}
  * @param {!WebInspector.Target} target
  */
 WebInspector.HeapProfilerModel = function(target)
 {
     WebInspector.SDKModel.call(this, WebInspector.HeapProfilerModel, target);
     target.registerHeapProfilerDispatcher(new WebInspector.HeapProfilerDispatcher(this));
     this._enabled = false;
     this._heapProfilerAgent = target.heapProfilerAgent();
 }
 
+/** @enum {symbol} */
 WebInspector.HeapProfilerModel.Events = {
-    HeapStatsUpdate: "HeapStatsUpdate",
-    LastSeenObjectId: "LastSeenObjectId",
-    AddHeapSnapshotChunk: "AddHeapSnapshotChunk",
-    ReportHeapSnapshotProgress: "ReportHeapSnapshotProgress",
-    ResetProfiles: "ResetProfiles"
+    HeapStatsUpdate: Symbol("HeapStatsUpdate"),
+    LastSeenObjectId: Symbol("LastSeenObjectId"),
+    AddHeapSnapshotChunk: Symbol("AddHeapSnapshotChunk"),
+    ReportHeapSnapshotProgress: Symbol("ReportHeapSnapshotProgress"),
+    ResetProfiles: Symbol("ResetProfiles")
 }
 
 WebInspector.HeapProfilerModel.prototype = {
     enable: function()
     {
         if (this._enabled)
             return;
 
         this._enabled = true;
         this._heapProfilerAgent.enable();
@@ skipping 110 matching lines @@
     },
 
     /**
      * @override
      */
     resetProfiles: function()
     {
         this._heapProfilerModel.resetProfiles();
     }
 }