Make style building for font-weight less custom.

Source/core/css/resolver/StyleBuilderConverter.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
  * copyright notice, this list of conditions and the following disclaimer
  * in the documentation and/or other materials provided with the
  * distribution.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 72 matching lines @@
 }
 
 AtomicString StyleBuilderConverter::convertFragmentIdentifier(StyleResolverState& state, CSSValue* value)
 {
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     if (primitiveValue->isURI())
         return SVGURIReference::fragmentIdentifierFromIRIString(primitiveValue->getStringValue(), state.element()->treeScope());
     return nullAtom;
 }
 
+FontWeight StyleBuilderConverter::convertFontWeight(StyleResolverState& state, CSSValue* value)
+{
+    CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
+    switch (primitiveValue->getValueID()) {
+    case CSSValueBolder:
+        return FontDescription::bolderWeight(state.parentStyle()->fontDescription().weight());
+    case CSSValueLighter:
+        return FontDescription::lighterWeight(state.parentStyle()->fontDescription().weight());
+    default:
+        return *primitiveValue;
+    }
+}
+
 FontDescription::VariantLigatures StyleBuilderConverter::convertFontVariantLigatures(StyleResolverState&, CSSValue* value)
 {
     if (value->isValueList()) {
         FontDescription::VariantLigatures ligatures;
         CSSValueList* valueList = toCSSValueList(value);
         for (size_t i = 0; i < valueList->length(); ++i) {
             CSSValue* item = valueList->item(i);
             CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(item);
             switch (primitiveValue->getValueID()) {
             case CSSValueNoCommonLigatures:
@@ skipping 393 matching lines @@
 {
     CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
     if (primitiveValue->getValueID()) {
         float multiplier = convertLineWidth<float>(state, value);
         return CSSPrimitiveValue::create(multiplier / 48, CSSPrimitiveValue::CSS_EMS)->computeLength<float>(state.cssToLengthConversionData());
     }
     return primitiveValue->computeLength<float>(state.cssToLengthConversionData());
 }
 
 } // namespace blink