Reduce CSSProperty's StylePropertyMetadata memory footprint by half when used inside a ImmutableSty…

Source/core/css/CSSParser.cpp

Index: Source/core/css/CSSParser.cpp
diff --git a/Source/core/css/CSSParser.cpp b/Source/core/css/CSSParser.cpp
index 3a923df744919175dc56c4b48b2f5236843d9016..1511cfde1f79376b76dfeb263faff625d294f126 100644
--- a/Source/core/css/CSSParser.cpp
+++ b/Source/core/css/CSSParser.cpp
@@ -1394,12 +1394,32 @@ void CSSParser::addPropertyWithPrefixingVariant(CSSPropertyID propId, PassRefPtr
     CSSPropertyID prefixingVariant = prefixingVariantForPropertyId(propId);
     if (prefixingVariant == propId)
         return;
-    addProperty(prefixingVariant, val.release(), important, implicit);
+
+    if (m_currentShorthand) {
+        // We can't use ShorthandScope here as we can already be inside one (e.g we are parsing CSSTransition).
+        m_currentShorthand = prefixingVariantForPropertyId(m_currentShorthand);
+        addProperty(prefixingVariant, val.release(), important, implicit);
+        m_currentShorthand = prefixingVariantForPropertyId(m_currentShorthand);
+    } else {
+        addProperty(prefixingVariant, val.release(), important, implicit);
+    }
 }
 
 void CSSParser::addProperty(CSSPropertyID propId, PassRefPtr<CSSValue> value, bool important, bool implicit)
 {
-    m_parsedProperties.append(CSSProperty(propId, value, important, m_currentShorthand, m_implicitShorthand || implicit));
+    CSSPrimitiveValue* primitiveValue = value->isPrimitiveValue() ? toCSSPrimitiveValue(value.get()) : 0;
+    // This property doesn't belong to a shorthand or is a CSS variable (which will be resolved later).
+    if (!m_currentShorthand || (primitiveValue && primitiveValue->isVariableName())) {
+        m_parsedProperties.append(CSSProperty(propId, value, important, false, CSSPropertyInvalid, m_implicitShorthand || implicit));
+        return;
+    }
+
+    const Vector<StylePropertyShorthand> shorthands = matchingShorthandsForLonghand(propId);
+    // The longhand does not belong to multiple shorthands.
+    if (shorthands.size() == 1)
+        m_parsedProperties.append(CSSProperty(propId, value, important, true, CSSPropertyInvalid, m_implicitShorthand || implicit));
+    else
+        m_parsedProperties.append(CSSProperty(propId, value, important, true, indexOfShorthandForLonghand(m_currentShorthand, shorthands), m_implicitShorthand || implicit));
 }
 
 void CSSParser::rollbackLastProperties(int num)