Improve CSS Style matching spec compliance

Source/core/css/FontFaceCache.cpp

Index: Source/core/css/FontFaceCache.cpp
diff --git a/Source/core/css/FontFaceCache.cpp b/Source/core/css/FontFaceCache.cpp
index 85fac6f8e4f5e193997126af5fe9f3e4fbb0d633..79f4ceeb3eeda98cb902f71de339c4c623b6c075 100644
--- a/Source/core/css/FontFaceCache.cpp
+++ b/Source/core/css/FontFaceCache.cpp
@@ -32,6 +32,7 @@
 #include "core/css/CSSSegmentedFontFace.h"
 #include "core/css/CSSValueList.h"
 #include "core/css/FontFace.h"
+#include "core/css/FontStyleMatcher.h"
 #include "core/css/StyleRule.h"
 #include "core/fetch/FontResource.h"
 #include "core/fetch/ResourceFetcher.h"
@@ -39,6 +40,7 @@
 #include "platform/fonts/FontDescription.h"
 #include "wtf/text/AtomicString.h"
 
+
 namespace blink {
 
 FontFaceCache::FontFaceCache()
@@ -127,79 +129,6 @@ void FontFaceCache::clearAll()
     ++m_version;
 }
 
-static inline bool compareFontFaces(CSSSegmentedFontFace* first, CSSSegmentedFontFace* second, FontTraits desiredTraits)
-{
-    const FontTraits& firstTraits = first->traits();
-    const FontTraits& secondTraits = second->traits();
-
-    bool firstHasDesiredVariant = firstTraits.variant() == desiredTraits.variant();
-    bool secondHasDesiredVariant = secondTraits.variant() == desiredTraits.variant();
-
-    if (firstHasDesiredVariant != secondHasDesiredVariant)
-        return firstHasDesiredVariant;
-
-    // We need to check font-variant css property for CSS2.1 compatibility.
-    if (desiredTraits.variant() == FontVariantSmallCaps) {
-        // Prefer a font that has indicated that it can only support small-caps to a font that claims to support
-        // all variants. The specialized font is more likely to be true small-caps and not require synthesis.
-        bool firstRequiresSmallCaps = firstTraits.variant() == FontVariantSmallCaps;
-        bool secondRequiresSmallCaps = secondTraits.variant() == FontVariantSmallCaps;
-        if (firstRequiresSmallCaps != secondRequiresSmallCaps)
-            return firstRequiresSmallCaps;
-    }
-
-    bool firstHasDesiredStyle = firstTraits.style() == desiredTraits.style();
-    bool secondHasDesiredStyle = secondTraits.style() == desiredTraits.style();
-
-    if (firstHasDesiredStyle != secondHasDesiredStyle)
-        return firstHasDesiredStyle;
-
-    if (desiredTraits.style() == FontStyleItalic) {
-        // Prefer a font that has indicated that it can only support italics to a font that claims to support
-        // all styles. The specialized font is more likely to be the one the author wants used.
-        bool firstRequiresItalics = firstTraits.style() == FontStyleItalic;
-        bool secondRequiresItalics = secondTraits.style() == FontStyleItalic;
-        if (firstRequiresItalics != secondRequiresItalics)
-            return firstRequiresItalics;
-    }
-    if (secondTraits.weight() == desiredTraits.weight())
-        return false;
-
-    if (firstTraits.weight() == desiredTraits.weight())
-        return true;
-
-    // http://www.w3.org/TR/2011/WD-css3-fonts-20111004/#font-matching-algorithm says :
-    //   - If the desired weight is less than 400, weights below the desired weight are checked in descending order followed by weights above the desired weight in ascending order until a match is found.
-    //   - If the desired weight is greater than 500, weights above the desired weight are checked in ascending order followed by weights below the desired weight in descending order until a match is found.
-    //   - If the desired weight is 400, 500 is checked first and then the rule for desired weights less than 400 is used.
-    //   - If the desired weight is 500, 400 is checked first and then the rule for desired weights less than 400 is used.
-    static const unsigned fallbackRuleSets = 9;
-    static const unsigned rulesPerSet = 8;
-    static const FontWeight weightFallbackRuleSets[fallbackRuleSets][rulesPerSet] = {
-        { FontWeight200, FontWeight300, FontWeight400, FontWeight500, FontWeight600, FontWeight700, FontWeight800, FontWeight900 },
-        { FontWeight100, FontWeight300, FontWeight400, FontWeight500, FontWeight600, FontWeight700, FontWeight800, FontWeight900 },
-        { FontWeight200, FontWeight100, FontWeight400, FontWeight500, FontWeight600, FontWeight700, FontWeight800, FontWeight900 },
-        { FontWeight500, FontWeight300, FontWeight200, FontWeight100, FontWeight600, FontWeight700, FontWeight800, FontWeight900 },
-        { FontWeight400, FontWeight300, FontWeight200, FontWeight100, FontWeight600, FontWeight700, FontWeight800, FontWeight900 },
-        { FontWeight700, FontWeight800, FontWeight900, FontWeight500, FontWeight400, FontWeight300, FontWeight200, FontWeight100 },
-        { FontWeight800, FontWeight900, FontWeight600, FontWeight500, FontWeight400, FontWeight300, FontWeight200, FontWeight100 },
-        { FontWeight900, FontWeight700, FontWeight600, FontWeight500, FontWeight400, FontWeight300, FontWeight200, FontWeight100 },
-        { FontWeight800, FontWeight700, FontWeight600, FontWeight500, FontWeight400, FontWeight300, FontWeight200, FontWeight100 }
-    };
-
-    unsigned ruleSetIndex = static_cast<unsigned>(desiredTraits.weight());
-    ASSERT(ruleSetIndex < fallbackRuleSets);
-    const FontWeight* weightFallbackRule = weightFallbackRuleSets[ruleSetIndex];
-    for (unsigned i = 0; i < rulesPerSet; ++i) {
-        if (secondTraits.weight() == weightFallbackRule[i])
-            return false;
-        if (firstTraits.weight() == weightFallbackRule[i])
-            return true;
-    }
-
-    return false;
-}
-
 CSSSegmentedFontFace* FontFaceCache::get(const FontDescription& fontDescription, const AtomicString& family)
 {
     TraitsMap* familyFontFaces = m_fontFaces.get(family);
@@ -215,12 +144,8 @@ CSSSegmentedFontFace* FontFaceCache::get(const FontDescription& fontDescription,
     if (!faceResult.storedValue->value) {
         for (const auto& item : *familyFontFaces) {
             CSSSegmentedFontFace* candidate = item.value.get();
-            FontTraits candidateTraits = candidate->traits();
-            if (traits.style() == FontStyleNormal && candidateTraits.style() != FontStyleNormal)
-                continue;
-            if (traits.variant() == FontVariantNormal && candidateTraits.variant() != FontVariantNormal)
-                continue;
-            if (!faceResult.storedValue->value || compareFontFaces(candidate, faceResult.storedValue->value.get(), traits))
+            FontStyleMatcher styleMatcher(traits);
+            if (!faceResult.storedValue->value || styleMatcher.isCandidateBetter(candidate, faceResult.storedValue->value.get()))
                 faceResult.storedValue->value = candidate;
         }
     }