Make style building for 'font-size' less custom.

Source/core/editing/EditingStyle.cpp

 /*
  * Copyright (C) 2007, 2008, 2009 Apple Computer, Inc.
  * Copyright (C) 2010, 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 1620 matching lines @@
 {
     return value->isFontIndependentLength();
 }
 
 int legacyFontSizeFromCSSValue(Document* document, CSSPrimitiveValue* value, FixedPitchFontType fixedPitchFontType, LegacyFontSizeMode mode)
 {
     if (isCSSValueLength(value)) {
         int pixelFontSize = value->getIntValue(CSSPrimitiveValue::CSS_PX);
         int legacyFontSize = FontSize::legacyFontSize(document, pixelFontSize, fixedPitchFontType);
         // Use legacy font size only if pixel value matches exactly to that of legacy font size.
-        CSSValueID cssPrimitiveEquivalent = static_cast<CSSValueID>(legacyFontSize - 1 + CSSValueXSmall);
-        if (mode == AlwaysUseLegacyFontSize || FontSize::fontSizeForKeyword(document, cssPrimitiveEquivalent, fixedPitchFontType) == pixelFontSize)
+        if (mode == AlwaysUseLegacyFontSize || FontSize::fontSizeForKeyword(document, legacyFontSize, fixedPitchFontType) == pixelFontSize)
             return legacyFontSize;
 
         return 0;
     }
 
     if (CSSValueXSmall <= value->getValueID() && value->getValueID() <= CSSValueWebkitXxxLarge)
         return value->getValueID() - CSSValueXSmall + 1;
 
     return 0;
 }
@@ skipping 26 matching lines @@
 {
     for (Node* ancestor = node; ancestor; ancestor = ancestor->parentNode()) {
         RefPtrWillBeRawPtr<CSSComputedStyleDeclaration> ancestorStyle = CSSComputedStyleDeclaration::create(ancestor);
         if (!hasTransparentBackgroundColor(ancestorStyle.get()))
             return ancestorStyle->getPropertyCSSValue(CSSPropertyBackgroundColor);
     }
     return nullptr;
 }
 
 }