Extend srcset's syntax to include 'w' descriptors

Source/core/html/HTMLImageElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010 Apple Inc. All rights reserved.
  * Copyright (C) 2010 Google 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 137 matching lines @@
     }
 }
 
 void HTMLImageElement::parseAttribute(const QualifiedName& name, const AtomicString& value)
 {
     if (name == altAttr) {
         if (renderer() && renderer()->isImage())
             toRenderImage(renderer())->updateAltText();
     } else if (name == srcAttr || name == srcsetAttr) {
         if (RuntimeEnabledFeatures::srcsetEnabled()) {
-            ImageCandidate candidate = bestFitSourceForImageAttributes(document().devicePixelRatio(), fastGetAttribute(srcAttr), fastGetAttribute(srcsetAttr));
+            int effectiveSize = -1; // FIXME - hook up the real value from `sizes`
+            ImageCandidate candidate = bestFitSourceForImageAttributes(document().devicePixelRatio(), effectiveSize, fastGetAttribute(srcAttr), fastGetAttribute(srcsetAttr));
             m_bestFitImageURL = candidate.toAtomicString();
             float candidateScaleFactor = candidate.scaleFactor();
             if (candidateScaleFactor > 0)
                 m_imageDevicePixelRatio = 1 / candidateScaleFactor;
             if (renderer() && renderer()->isImage())
                 toRenderImage(renderer())->setImageDevicePixelRatio(m_imageDevicePixelRatio);
         }
         m_imageLoader.updateFromElementIgnoringPreviousError();
     } else if (name == usemapAttr) {
         setIsLink(!value.isNull());
@@ skipping 297 matching lines @@
     if (!image)
         return FloatSize();
     LayoutSize size;
     size = image->imageSizeForRenderer(renderer(), 1.0f); // FIXME: Not sure about this.
     if (renderer() && renderer()->isRenderImage() && image->image() && !image->image()->hasRelativeWidth())
         size.scale(toRenderImage(renderer())->imageDevicePixelRatio());
     return size;
 }
 
 }