DevTools: [regression] entering invalid property value in the styles sidebar results in exception.

Source/devtools/front_end/elements/StylesSidebarPane.js

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * 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
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 2592 matching lines @@
     kickFreeFlowStyleEditForTest: function()
     {
         this._applyFreeFlowStyleTextEdit();
     },
 
     /**
      * @param {!WebInspector.StylePropertyTreeElement.Context} context
      */
     editingEnded: function(context)
     {
-        delete this._originalPropertyText;
         this._resetMouseDownElement();
 
         this.setExpandable(context.hasChildren);
         if (context.expanded)
             this.expand();
         var editedElement = context.isEditingName ? this.nameElement : this.valueElement;
         // The proxyElement has been deleted, no need to remove listener.
         if (editedElement.parentElement)
             editedElement.parentElement.classList.remove("child-editing");
 
         this._parentPane.setEditingStyle(false);
     },
 
     /**
      * @param {?Element} element
      * @param {!WebInspector.StylePropertyTreeElement.Context} context
      */
     editingCancelled: function(element, context)
     {
         this._removePrompt();
         this._revertStyleUponEditingCanceled();
         // This should happen last, as it clears the info necessary to restore the property value after [Page]Up/Down changes.
         this.editingEnded(context);
     },
 
     _revertStyleUponEditingCanceled: function()
     {
-        if (this._propertyHasBeenEditedIncrementally)
+        if (this._propertyHasBeenEditedIncrementally) {
             this.applyStyleText(this._originalPropertyText, false);
-        else if (this._newProperty)
+            delete this._originalPropertyText;
+        } else if (this._newProperty) {
             this.treeOutline.removeChild(this);
-        else
+        } else {
             this.updateTitle();
+        }
     },
 
     /**
      * @param {string} moveDirection
      * @return {?WebInspector.StylePropertyTreeElement}
      */
     _findSibling: function(moveDirection)
     {
         var target = this;
         do {
@@ skipping 593 matching lines @@
 
     /**
      * @override
      * @return {?WebInspector.ToolbarItem}
      */
     item: function()
     {
         return this._button;
     }
 }