Fix resolving protocol-agnostic <svg:image> URLs in about:blank iframes

Source/core/svg/SVGImageLoader.cpp

 /*
  * Copyright (C) 2005, 2005 Alexander Kellett <lypanov@kde.org>
  * Copyright (C) 2008 Rob Buis <buis@kde.org>
  *
  * 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,
@@ skipping 29 matching lines @@
         element()->dispatchEvent(Event::create(EventTypeNames::error));
     else {
         SVGImageElement* imageElement = toSVGImageElement(element());
         imageElement->sendSVGLoadEventIfPossible(true);
     }
 }
 
 String SVGImageLoader::sourceURI(const AtomicString& attribute) const
 {
     KURL base = element()->baseURI();
-    if (base.isValid())
-        return KURL(base, stripLeadingAndTrailingHTMLSpaces(attribute)).string();
-    return element()->document().completeURL(stripLeadingAndTrailingHTMLSpaces(attribute));
+    if (!base.isValid())
+        base = element()->document().baseURI();
+    return element()->document().completeURLWithOverride(stripLeadingAndTrailingHTMLSpaces(attribute), base);
 }
 
 }