Align srcset parsing with spec changed

This CL align the srcset parsing algorithm with recent picture spec changes.
Specifically:
* Src URL are now not part of the source selection algoritm, as per https://github.com/ResponsiveImagesCG/picture-element/pull/147
* 0w resources are ignored, to avoid 0/0 operations, and because they make no sense, as per https://github.com/ResponsiveImagesCG/picture-element/pull/151

BUG=357586

Review URL: https://codereview.chromium.org/236593003

git-svn-id: svn://svn.chromium.org/blink/trunk@171489 bbb929c8-8fbe-4397-9dbb-9b2b20218538

third_party/WebKit/Source/core/html/parser/HTMLSrcsetParser.cpp

@@ -75,7 +75,7 @@ static bool parseDescriptors(const CharType* descriptorsStart, const CharType* d
             if (result.foundDescriptor())
                 return false;
             result.resourceWidth = charactersToInt(currentDescriptorStart, descriptorLength, &isValid);
-            if (!isValid || result.resourceWidth < 0)
+            if (!isValid || result.resourceWidth <= 0)
                 return false;
         }
     }
@@ -122,7 +122,11 @@ static void parseImageCandidatesFromSrcsetAttribute(const String& attribute, con
                 continue;
         }
 
-        imageCandidates.append(ImageCandidate(attribute, imageURLStart - attributeStart, imageURLEnd - imageURLStart, result));
+        ASSERT(imageURLEnd > attributeStart);
+        unsigned imageURLStartingPosition = imageURLStart - attributeStart;
+        ASSERT(imageURLEnd > imageURLStart);
+        unsigned imageURLLength = imageURLEnd - imageURLStart;
+        imageCandidates.append(ImageCandidate(attribute, imageURLStartingPosition, imageURLLength, result, ImageCandidate::SrcsetOrigin));
         // 11. Return to the step labeled splitting loop.
     }
 }
@@ -140,20 +144,23 @@ static void parseImageCandidatesFromSrcsetAttribute(const String& attribute, Vec
 
 static ImageCandidate pickBestImageCandidate(float deviceScaleFactor, int effectiveSize, Vector<ImageCandidate>& imageCandidates)
 {
+    bool ignoreSrc = false;
     if (imageCandidates.isEmpty())
         return ImageCandidate();
 
     // http://picture.responsiveimages.org/#normalize-source-densities
     for (Vector<ImageCandidate>::iterator it = imageCandidates.begin(); it != imageCandidates.end(); ++it) {
-        if (it->scaleFactor() < 0)
+        if (it->resourceWidth() > 0) {
             it->setScaleFactor((float)it->resourceWidth() / (float)effectiveSize);
+            ignoreSrc = true;
+        }
     }
 
     std::stable_sort(imageCandidates.begin(), imageCandidates.end(), compareByScaleFactor);
 
     unsigned i;
     for (i = 0; i < imageCandidates.size() - 1; ++i) {
-        if (imageCandidates[i].scaleFactor() >= deviceScaleFactor)
+        if ((imageCandidates[i].scaleFactor() >= deviceScaleFactor) && (!ignoreSrc || !imageCandidates[i].srcOrigin()))
             break;
     }
 
@@ -184,7 +191,7 @@ ImageCandidate bestFitSourceForImageAttributes(float deviceScaleFactor, int effe
     if (srcsetAttribute.isNull()) {
         if (srcAttribute.isNull())
             return ImageCandidate();
-        return ImageCandidate(srcAttribute, 0, srcAttribute.length(), defaultResult);
+        return ImageCandidate(srcAttribute, 0, srcAttribute.length(), defaultResult, ImageCandidate::SrcOrigin);
     }
 
     Vector<ImageCandidate> imageCandidates;
@@ -192,7 +199,7 @@ ImageCandidate bestFitSourceForImageAttributes(float deviceScaleFactor, int effe
     parseImageCandidatesFromSrcsetAttribute(srcsetAttribute, imageCandidates);
 
     if (!srcAttribute.isEmpty())
-        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), defaultResult));
+        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), defaultResult, ImageCandidate::SrcOrigin));
 
     return pickBestImageCandidate(deviceScaleFactor, effectiveSize, imageCandidates);
 }
@@ -209,7 +216,7 @@ String bestFitSourceForImageAttributes(float deviceScaleFactor, int effectiveSiz
     imageCandidates.append(srcsetImageCandidate);
 
     if (!srcAttribute.isEmpty())
-        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), defaultResult));
+        imageCandidates.append(ImageCandidate(srcAttribute, 0, srcAttribute.length(), defaultResult, ImageCandidate::SrcOrigin));
 
     return pickBestImageCandidate(deviceScaleFactor, effectiveSize, imageCandidates).toString();
 }

third_party/WebKit/Source/core/html/parser/HTMLSrcsetParser.h

@@ -53,15 +53,21 @@ struct DescriptorParsingResult {
 
 class ImageCandidate {
 public:
+    enum OriginAttribute {
+        SrcsetOrigin,
+        SrcOrigin
+    };
+
     ImageCandidate()
         : m_scaleFactor(1.0)
     {
     }
 
-    ImageCandidate(const String& source, unsigned start, unsigned length, const DescriptorParsingResult& result)
+    ImageCandidate(const String& source, unsigned start, unsigned length, const DescriptorParsingResult& result, OriginAttribute originAttribute)
         : m_string(source.createView(start, length))
         , m_scaleFactor(result.scaleFactor)
         , m_resourceWidth(result.resourceWidth)
+        , m_originAttribute(originAttribute)
     {
     }
 
@@ -90,6 +96,11 @@ public:
         return m_resourceWidth;
     }
 
+    bool srcOrigin() const
+    {
+        return (m_originAttribute == SrcOrigin);
+    }
+
     inline bool isEmpty() const
     {
         return m_string.isEmpty();
@@ -99,6 +110,7 @@ private:
     StringView m_string;
     float m_scaleFactor;
     int m_resourceWidth;
+    OriginAttribute m_originAttribute;
 };
 
 ImageCandidate bestFitSourceForSrcsetAttribute(float deviceScaleFactor, int effectiveSize, const String& srcsetAttribute);

third_party/WebKit/Source/core/html/parser/HTMLSrcsetParserTest.cpp

@@ -46,6 +46,12 @@ TEST(HTMLSrcsetParserTest, Basic)
         {5.0, -1, "", "1x,,  ,   x    ,2x  , 1x.gif, 3x, 4x.gif 4x 100h, 5x.gif 5, dx.gif dx, 2x.gif   2x ,", "4x.gif", 4.0, -1},
         {1.0, 400, "", "400.gif 400w, 6000.gif 6000w", "400.gif", 1.0, 400},
         {2.0, 400, "", "400.gif 400w, 6000.gif 6000w", "6000.gif", 15.0, 6000},
+        {1.0, 400, "src.gif", "800.gif 800w", "800.gif", 2.0, 800},
+        {1.0, 400, "src.gif", "0.gif 0w, 800.gif 800w", "800.gif", 2.0, 800},
+        {1.0, 400, "src.gif", "0.gif 0w, 2x.gif 2x", "src.gif", 1.0, -1},
+        {1.0, 400, "src.gif", "800.gif 2x, 1600.gif 1600w", "800.gif", 2.0, -1},
+        {1.0, 400, "", "400.gif 400w, 2x.gif 2x", "400.gif", 1.0, 400},
+        {2.0, 400, "", "400.gif 400w, 2x.gif 2x", "2x.gif", 2.0, -1},
         {1.0, 0, "", "400.gif 400w, 6000.gif 6000w", "400.gif", std::numeric_limits<float>::infinity(), 400},
         {0, 0, 0, 0, 0, 0} // Do not remove the terminator line.
     };