DevTools: workaround bug in Blink selection API

third_party/WebKit/Source/devtools/front_end/platform/DOMExtension.js

 /*
  * Copyright (C) 2007 Apple Inc.  All rights reserved.
  * 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:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
@@ skipping 330 matching lines @@
     if (this.firstChild)
         this.textContent = "";
 }
 
 /**
  * @return {boolean}
  */
 Element.prototype.isInsertionCaretInside = function()
 {
     var selection = this.getComponentSelection();
-    if (!selection.rangeCount || !selection.isCollapsed)
+    // @see crbug.com/602541
+    var selectionRange = selection && selection.rangeCount ? selection.getRangeAt(0) : null;
+    if (!selectionRange || !selection.isCollapsed)
         return false;
-    var selectionRange = selection.getRangeAt(0);
     return selectionRange.startContainer.isSelfOrDescendant(this);
 }
 
 /**
  * @param {string} tagName
  * @param {string=} customElementType
  * @return {!Element}
  * @suppressGlobalPropertiesCheck
  */
 function createElement(tagName, customElementType)
@@ skipping 621 matching lines @@
     {
         window.removeEventListener("DOMContentLoaded", windowLoaded, false);
         callback();
     }
 
     if (document.readyState === "complete" || document.readyState === "interactive")
         callback();
     else
         window.addEventListener("DOMContentLoaded", windowLoaded, false);
 }