Implement the 'noopener' window feature.

third_party/WebKit/Source/core/frame/Window.idl

 /*
  * Copyright (C) 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 44 matching lines @@
 
     // other browsing contexts
     [Replaceable, DoNotCheckSecurity] readonly attribute Window frames;
     [Replaceable, DoNotCheckSecurity] readonly attribute unsigned long length;
     [Unforgeable, DoNotCheckSecurity] readonly attribute Window top;
     // FIXME: opener should be of type any.
     [DoNotCheckSecurity, Custom=Setter] attribute Window opener;
     [Replaceable, DoNotCheckSecurity] readonly attribute Window parent;
     [CheckSecurity=Node, Custom=Getter] readonly attribute Element? frameElement;
     // FIXME: open() should have 4 optional arguments with defaults.
-    [Custom] Window open(DOMString url, DOMString target, optional DOMString features);
+    [Custom] Window? open(DOMString url, DOMString target, optional DOMString features);
     // FIXME: These getters should not have [NotEnumerable].
     [NotEnumerable, DoNotCheckSecurity] getter Window (unsigned long index);
     [Custom, NotEnumerable, DoNotCheckSecurity] getter object (DOMString name);
 
     // the user agent
     [LogActivity=GetterOnly] readonly attribute Navigator navigator;
     [RuntimeEnabled=ApplicationCache, LogActivity=GetterOnly] readonly attribute ApplicationCache applicationCache;
 
     // user prompts
     [Measure] void alert();
@@ skipping 124 matching lines @@
 // FIXME: make this typedef accurate once enough of http://crbug.com/240176
 // is in place.
 // FIXME: consider putting this typedef in an .idl file containing spec-wide
 // utility type definitions.
 typedef MessagePort Transferable;
 
 Window implements GlobalEventHandlers;
 Window implements WindowBase64;
 Window implements WindowEventHandlers;
 Window implements WindowTimers;