Fixed srcset descriptor parsing bug and added tests

Source/core/html/parser/HTMLSrcsetParser.cpp

 /*
  * Copyright (C) 2013 Apple Inc. All rights reserved.
  * 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.
@@ skipping 49 matching lines @@
     }
 
     unsigned lastIndex()
     {
         return start + length - 1;
     }
 
     template<typename CharType>
     int toInt(const CharType* attribute, bool& isValid)
     {
-        return charactersToInt(attribute + start, length - 1, &isValid);
+        return charactersToIntStrict(attribute + start, length - 1, &isValid);
     }
 
     template<typename CharType>
     float toFloat(const CharType* attribute, bool& isValid)
     {
         return charactersToFloat(attribute + start, length - 1, &isValid);
     }
 };
 
 template<typename CharType>
@@ skipping 260 matching lines @@
     Vector<ImageCandidate> imageCandidates;
     imageCandidates.append(srcsetImageCandidate);
 
     if (!srcAttribute.isEmpty())
         imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), DescriptorParsingResult(), ImageCandidate::SrcOrigin));
 
     return pickBestImageCandidate(deviceScaleFactor, sourceSize, imageCandidates).toString();
 }
 
 }