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

Source/platform/fonts/FontDescription.cpp

 /*
  * Copyright (C) 2007 Nicholas Shanks <contact@nickshanks.com>
  * Copyright (C) 2008 Apple 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.
@@ skipping 78 matching lines @@
         case FontWeight600:
         case FontWeight700:
         case FontWeight800:
         case FontWeight900:
             return FontWeight900;
     }
     ASSERT_NOT_REACHED();
     return FontWeightNormal;
 }
 
+FontDescription::Size FontDescription::largerSize(const Size& size)
+{
+    return Size(0, size.value * 1.2, size.isAbsolute);
+}
+
+FontDescription::Size FontDescription::smallerSize(const Size& size)
+{
+    return Size(0, size.value / 1.2, size.isAbsolute);
+}
+
 FontTraits FontDescription::traits() const
 {
     return FontTraits(style(), variant(), weight(), stretch());
 }
 
 FontDescription::VariantLigatures FontDescription::variantLigatures() const
 {
     VariantLigatures ligatures;
 
     ligatures.common = commonLigaturesState();
@@ skipping 104 matching lines @@
 
         if (discretionaryLigaturesState() == FontDescription::EnabledLigaturesState
             || historicalLigaturesState() == FontDescription::EnabledLigaturesState
             || contextualLigaturesState() == FontDescription::EnabledLigaturesState) {
             m_typesettingFeatures |= blink::Ligatures;
         }
     }
 }
 
 } // namespace blink