Make style building for font-weight less custom.

Source/platform/fonts/FontDescription.cpp

Index: Source/platform/fonts/FontDescription.cpp
diff --git a/Source/platform/fonts/FontDescription.cpp b/Source/platform/fonts/FontDescription.cpp
index 829d815d24a66b92979278a8484d180831b93b64..7c45aea2db23f673e9609a554659d1c26bce974a 100644
--- a/Source/platform/fonts/FontDescription.cpp
+++ b/Source/platform/fonts/FontDescription.cpp
@@ -52,9 +52,9 @@ TypesettingFeatures FontDescription::s_defaultTypesettingFeatures = 0;
 
 bool FontDescription::s_useSubpixelTextPositioning = false;
 
-FontWeight FontDescription::lighterWeight(void) const
+FontWeight FontDescription::lighterWeight(FontWeight weight)
 {
-    switch (m_weight) {
+    switch (weight) {
         case FontWeight100:
         case FontWeight200:
         case FontWeight300:
@@ -74,9 +74,9 @@ FontWeight FontDescription::lighterWeight(void) const
     return FontWeightNormal;
 }
 
-FontWeight FontDescription::bolderWeight(void) const
+FontWeight FontDescription::bolderWeight(FontWeight weight)
 {
-    switch (m_weight) {
+    switch (weight) {
         case FontWeight100:
         case FontWeight200:
         case FontWeight300: