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

Source/core/css/FontSize.h

Index: Source/core/css/FontSize.h
diff --git a/Source/core/css/FontSize.h b/Source/core/css/FontSize.h
index a864114419e9bd87da50201fb01054c4cbb63236..79ad500456c9e36fdca17d6b9e6f16cfd3b0802d 100644
--- a/Source/core/css/FontSize.h
+++ b/Source/core/css/FontSize.h
@@ -40,9 +40,19 @@ private:
 public:
     static float getComputedSizeFromSpecifiedSize(const Document*, float zoomFactor, bool isAbsoluteSize, float specifiedSize, ESmartMinimumForFontSize = UseSmartMinimumForFontFize);
 
-    // Given a CSS keyword in the range (xx-small to -webkit-xxx-large), this function will return
-    // the correct font size scaled relative to the user's default (medium).
-    static float fontSizeForKeyword(const Document*, CSSValueID keyword, FixedPitchFontType);
+    // Given a CSS keyword in the range (xx-small to -webkit-xxx-large), this function returns
+    // values from '1' to '8'.
+    static unsigned keywordSize(CSSValueID valueID)
+    {
+        ASSERT(valueID >= CSSValueXxSmall && valueID <= CSSValueWebkitXxxLarge);
+        return valueID - CSSValueXxSmall + 1;
+    }
+
+    static unsigned initialKeywordSize() { return 4; } // CSSValueMedium
+
+    // Given a keyword size in the range (1 to 8), this function will return
+    // the correct font size scaled relative to the user's default (4).
+    static float fontSizeForKeyword(const Document*, unsigned keyword, FixedPitchFontType);
 
     // Given a font size in pixel, this function will return legacy font size between 1 and 7.
     static int legacyFontSize(const Document*, int pixelFontSize, FixedPitchFontType);