Refactor srcset parser to align it with spec changes

Source/core/html/parser/HTMLSrcsetParser.h

 /*
  * 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 18 matching lines @@
  */
 
 #ifndef HTMLSrcsetParser_h
 #define HTMLSrcsetParser_h
 
 #include "wtf/text/WTFString.h"
 
 namespace WebCore {
 
 struct DescriptorParsingResult {
-    float scaleFactor;
+    float density;
     int resourceWidth;
+    int resourceHeight;
 
     DescriptorParsingResult()
     {
-        scaleFactor = -1.0;
+        density = -1.0;

[eseidel, 2014/05/28 22:24:59]

Bleh.  Sentinel values/in-band data.  :(

You might want to make these have real accessors that ASSERT that they're not
called when these values are bad...  You may end up with very strange bugs if
someone grabs these and fails to check foundFoo.

[Yoav Weiss, 2014/05/29 05:17:40]

OK, I'll turn that into a class with proper getters.

         resourceWidth = -1;
+        resourceHeight = -1;
     }
 
-    bool foundDescriptor() const
-    {
-        return (scaleFactor >= 0 || resourceWidth >= 0);
-    }
+    bool foundDensity() { return density >= 0; }

[eseidel, 2014/05/28 22:24:59]

I think "hasDensitiy" might be more consistent with other code in blink, but
found can be OK if it matches the callers.  Up to you.

[Yoav Weiss, 2014/05/29 05:17:40]

Sure

+    bool foundWidth() { return resourceWidth >= 0; }

[eseidel, 2014/05/28 22:24:59]

Can these ever be set to negative numbers intentionally?  What should the
behavior be?  Do we need a setter which ignores negative values?  Ah, the
pit-falls of sentinal values.

[Yoav Weiss, 2014/05/29 05:17:40]

No
Yeah, I'll add that

+    bool foundHeight() { return resourceHeight >= 0; }
 };
 
 class ImageCandidate {
 public:
     enum OriginAttribute {
         SrcsetOrigin,
         SrcOrigin
     };
 
     ImageCandidate()
-        : m_scaleFactor(1.0)
+        : m_density(1.0)
     {
     }
 
     ImageCandidate(const String& source, unsigned start, unsigned length, const DescriptorParsingResult& result, OriginAttribute originAttribute)
         : m_string(source.createView(start, length))
-        , m_scaleFactor(result.scaleFactor)
+        , m_density(result.density)
         , m_resourceWidth(result.resourceWidth)
         , m_originAttribute(originAttribute)
     {
     }
 
     String toString() const
     {
         return String(m_string.toString());
     }
 
     AtomicString url() const
     {
         return AtomicString(m_string.toString());
     }
 
-    void setScaleFactor(float factor)
+    void setDensity(float factor)
     {
-        m_scaleFactor = factor;
+        m_density = factor;
     }
 
-    float scaleFactor() const
+    float density() const
     {
-        return m_scaleFactor;
+        return m_density;
     }
 
     int resourceWidth() const
     {
         return m_resourceWidth;
     }
 
     bool srcOrigin() const
     {
         return (m_originAttribute == SrcOrigin);
     }
 
     inline bool isEmpty() const
     {
         return m_string.isEmpty();
     }
 
 private:
     StringView m_string;
-    float m_scaleFactor;
+    float m_density;
     int m_resourceWidth;
     OriginAttribute m_originAttribute;
 };
 
 ImageCandidate bestFitSourceForSrcsetAttribute(float deviceScaleFactor, unsigned sourceSize, const String& srcsetAttribute);
 
 ImageCandidate bestFitSourceForImageAttributes(float deviceScaleFactor, unsigned sourceSize, const String& srcAttribute, const String& srcsetAttribute);
 
 String bestFitSourceForImageAttributes(float deviceScaleFactor, unsigned sourceSize, const String& srcAttribute, ImageCandidate& srcsetImageCandidate);
 
 }
 
 #endif