[DevTools] Remove Common.Event.target field.

third_party/WebKit/Source/devtools/front_end/elements/ElementsTreeOutline.js

 /*
  * Copyright (C) 2007, 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2008 Matt Lilek <webkit@mattlilek.com>
  * Copyright (C) 2009 Joseph Pecoraro
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
@@ skipping 1022 matching lines @@
   _updateRecordForHighlight(node) {
     if (!this._visible)
       return null;
     return this._updateRecords.get(node) || null;
   }
 
   /**
    * @param {!Common.Event} event
    */
   _documentUpdated(event) {
-    var inspectedRootDocument = event.data;
+    var domModel = /** @type {!SDK.DOMModel} */ (event.data);
+    var inspectedRootDocument = domModel.existingDocument();
 
     this._reset();
 
     if (!inspectedRootDocument)
       return;
 
     this.rootDOMNode = inspectedRootDocument;
   }
 
   /**
@@ skipping 639 matching lines @@
      */
     function resolved(node) {
       if (node) {
         this.treeOutline._selectedDOMNode = node;
         this.treeOutline._selectedNodeChanged();
       }
     }
     return true;
   }
 };