Enable srcset support in HTMLImageElement

Source/core/html/parser/HTMLParserIdioms.cpp

Index: Source/core/html/parser/HTMLParserIdioms.cpp
diff --git a/Source/core/html/parser/HTMLParserIdioms.cpp b/Source/core/html/parser/HTMLParserIdioms.cpp
index 6f136305f07ee01108d46d0b8da093bcfc11b83c..8902789e4e188aea1c271a253ee3b392e6c2a323 100644
--- a/Source/core/html/parser/HTMLParserIdioms.cpp
+++ b/Source/core/html/parser/HTMLParserIdioms.cpp
@@ -29,6 +29,7 @@
 #include "core/dom/QualifiedName.h"
 #include "core/html/parser/HTMLIdentifier.h"
 #include "core/platform/Decimal.h"
+#include "core/platform/text/DecodeEscapeSequences.h"
 #include "wtf/MathExtras.h"
 #include "wtf/text/AtomicString.h"
 #include "wtf/text/StringBuilder.h"
@@ -296,4 +297,74 @@ bool threadSafeMatch(const HTMLIdentifier& localName, const QualifiedName& qName
     return threadSafeEqual(localName.asStringImpl(), qName.localName().impl());
 }
 
+struct ImageWithScale {
+    String imageURL;
+    float scaleFactor;
+    bool operator==(const ImageWithScale& image) const
+    {
+        return scaleFactor == image.scaleFactor && imageURL == image.imageURL;
+    }
+};
+typedef Vector<ImageWithScale> ImageCandidates;
+
+static inline bool compareByScaleFactor(const ImageWithScale& first, const ImageWithScale& second)
+{
+    return first.scaleFactor < second.scaleFactor;
+}
+
+String bestFitSourceForImageAttributes(float deviceScaleFactor, const String& srcAttribute, const String& srcSetAttribute)
+{
+    ImageCandidates imageCandidates;
+
+    const String srcSetAttributeValue = srcSetAttribute.simplifyWhiteSpace(isHTMLSpace);
+    Vector<String> srcSetTokens;
+
+    srcSetAttributeValue.split(',', srcSetTokens);
+    for (size_t i = 0; i < srcSetTokens.size(); ++i) {
+        Vector<String> data;
+        float imgScaleFactor = 1.0;
+        bool validScaleFactor = false;
+
+        srcSetTokens[i].stripWhiteSpace().split(' ', data);
+        // There must be at least one candidate descriptor, and the last one must
+        // be a scale factor. Since we don't support descriptors other than scale,
+        // it's better to discard any rule with such descriptors rather than accept
+        // only the scale data.
+        if (data.size() != 2)
+            continue;
+        if (!data.last().endsWith('x'))
+            continue;
+
+        imgScaleFactor = data.last().substring(0, data.last().length() - 1).toFloat(&validScaleFactor);
+        if (!validScaleFactor)
+            continue;
+
+        ImageWithScale image;
+        image.imageURL = decodeEscapeSequences<URLEscapeSequence>(data[0], UTF8Encoding());
+        image.scaleFactor = imgScaleFactor;
+
+        imageCandidates.append(image);
+    }
+
+    const String src =  srcAttribute.simplifyWhiteSpace(isHTMLSpace);
+    if (!src.isEmpty()) {
+        ImageWithScale image;
+        image.imageURL = decodeEscapeSequences<URLEscapeSequence>(src, UTF8Encoding());
+        image.scaleFactor = 1.0;
+
+        imageCandidates.append(image);
+    }
+
+    if (imageCandidates.isEmpty())
+        return String();
+
+    std::stable_sort(imageCandidates.begin(), imageCandidates.end(), compareByScaleFactor);
+
+    for (size_t i = 0; i < imageCandidates.size() - 1; ++i) {
+        if (imageCandidates[i].scaleFactor >= deviceScaleFactor)
+            return imageCandidates[i].imageURL;
+    }
+    return imageCandidates.last().imageURL;
+}
+
 }