Expand system font values during font property parsing

Source/core/rendering/RenderTheme.cpp

Index: Source/core/rendering/RenderTheme.cpp
diff --git a/Source/core/rendering/RenderTheme.cpp b/Source/core/rendering/RenderTheme.cpp
index 972bcf6c11a8177510972e7bc259e6dcc554732b..66952fd6decb98b04c3280eb25c21de2608cf578 100644
--- a/Source/core/rendering/RenderTheme.cpp
+++ b/Source/core/rendering/RenderTheme.cpp
@@ -989,6 +989,21 @@ void RenderTheme::platformColorsDidChange()
     Page::scheduleForcedStyleRecalcForAllPages();
 }
 
+void RenderTheme::systemFont(CSSValueID systemFontID, FontDescription& fontDescription)
+{
+    FontStyle fontStyle = FontStyleNormal;
+    FontWeight fontWeight = FontWeightNormal;
+    float fontSize = 0;
+    AtomicString fontFamily;
+    systemFont(systemFontID, fontStyle, fontWeight, fontSize, fontFamily);
+    fontDescription.setStyle(fontStyle);
+    fontDescription.setWeight(fontWeight);
+    fontDescription.setSpecifiedSize(fontSize);
+    fontDescription.setIsAbsoluteSize(true);
+    fontDescription.firstFamily().setFamily(fontFamily);
+    fontDescription.setGenericFamily(FontDescription::NoFamily);
+}
+
 Color RenderTheme::systemColor(CSSValueID cssValueId) const
 {
     switch (cssValueId) {