[SVG2] Make ownerSVGElement and viewportElement nullable.

Source/core/svg/SVGElement.idl

 /*
  * Copyright (C) 2004, 2005 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005 Rob Buis <buis@kde.org>
  * Copyright (C) 2006 Samuel Weinig <sam.weinig@gmail.com>
  * Copyright (C) 2006 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  * Library General Public License for more details.
  *
  * You should have received a copy of the GNU Library General Public License
  * along with this library; see the file COPYING.LIB.  If not, write to
  * the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
  * Boston, MA 02110-1301, USA.
  */
 
 [
     Custom=Wrap,
 ] interface SVGElement : Element {
     attribute DOMString xmlbase;
-    readonly attribute SVGSVGElement ownerSVGElement;
-    readonly attribute SVGElement viewportElement;
+    [TypeChecking=Interface|Nullable] readonly attribute SVGSVGElement? ownerSVGElement;
+    [TypeChecking=Interface|Nullable] readonly attribute SVGElement? viewportElement;

[fs, 2014/05/26 13:05:42]

Note: This extended attribute will not "do anything" in this case (because of
the readonly - i.e. no setter), but it makes sense to add it nonetheless (IMHO).

[Erik Dahlström (inactive), 2014/05/26 13:13:35]

I followed the lead from HTMLMediaElement.idl, which had the same. I'll leave it
as is.

 
     attribute DOMString xmllang;
     attribute DOMString xmlspace;
 
     [MeasureAs=SVGClassName] readonly attribute SVGAnimatedString className;
 
     readonly attribute CSSStyleDeclaration style;
 
     [CustomElementCallbacks] attribute long tabIndex;
 };
 
 SVGElement implements GlobalEventHandlers;