Aligned srcset mixedContent blocking to the spec

Source/core/loader/ImageLoader.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2009, 2010 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.
  *
@@ skipping 224 matching lines @@
     if (!document.isActive())
         return;
 
     AtomicString imageSourceURL = m_element->imageSourceURL();
     KURL url = imageSourceToKURL(imageSourceURL);
     ResourcePtr<ImageResource> newImage = 0;
     if (!url.isNull()) {
         // Unlike raw <img>, we block mixed content inside of <picture> or <img srcset>.
         ResourceLoaderOptions resourceLoaderOptions = ResourceFetcher::defaultResourceOptions();
         ResourceRequest resourceRequest(url);
-        if (isHTMLPictureElement(element()->parentNode()) || !element()->fastGetAttribute(HTMLNames::srcsetAttr).isEmpty()) {
+        if (isHTMLPictureElement(element()->parentNode()) || !element()->fastGetAttribute(HTMLNames::srcsetAttr).isNull()) {
             resourceLoaderOptions.mixedContentBlockingTreatment = TreatAsActiveContent;
             resourceRequest.setRequestContext(WebURLRequest::RequestContextImageSet);
         }
         FetchRequest request(ResourceRequest(url), element()->localName(), resourceLoaderOptions);
         configureRequest(request, bypassBehavior, *m_element);
 
         if (m_loadingImageDocument)
             newImage = createImageResourceForImageDocument(document, request);
         else
             newImage = document.fetcher()->fetchImage(request);
@@ skipping 301 matching lines @@
 }
 
 #if ENABLE(OILPAN)
 ImageLoader::ImageLoaderClientRemover::~ImageLoaderClientRemover()
 {
     m_loader.willRemoveClient(m_client);
 }
 #endif
 
 }