Use srcset's resource pixel density to determine intrinsic size

Source/core/html/parser/HTMLSrcsetParser.cpp

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 136 matching lines @@
 
 ImageCandidate bestFitSourceForSrcsetAttribute(float deviceScaleFactor, const String& srcsetAttribute)
 {
     Vector<ImageCandidate> imageCandidates;
 
     parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);
 
     return pickBestImageCandidate(deviceScaleFactor, imageCandidates);
 }
 
-String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcsetAttribute)
+ImageCandidate bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcsetAttribute)
 {
-    if (srcsetAttribute.isNull())
-        return srcAttribute;
+    if (srcsetAttribute.isNull()) {
+        if (srcAttribute.isNull())
+            return ImageCandidate();
+        return ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1);
+    }
 
     Vector<ImageCandidate> imageCandidates;
 
     parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);
 
     if (!srcAttribute.isEmpty())
         imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1.0));
 
-    return pickBestImageCandidate(deviceScaleFactor, imageCandidates).toString();
+    return pickBestImageCandidate(deviceScaleFactor, imageCandidates);
 }
 
 String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, ImageCandidate& srcsetImageCandidate)
 {
     if (srcsetImageCandidate.isEmpty())
         return srcAttribute;
 
     Vector<ImageCandidate> imageCandidates;
     imageCandidates.append(srcsetImageCandidate);
 
     if (!srcAttribute.isEmpty())
         imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), 1.0));
 
     return pickBestImageCandidate(deviceScaleFactor, imageCandidates).toString();
 }
 
 }