Fixing superscript and subscript baseline for tiny fonts in SVG

third_party/WebKit/Source/core/layout/svg/SVGTextLayoutEngineBaseline.cpp

 /*
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 16 matching lines @@
 
 SVGTextLayoutEngineBaseline::SVGTextLayoutEngineBaseline(const Font& font,
                                                          float effectiveZoom)
     : m_font(font), m_effectiveZoom(effectiveZoom) {
   ASSERT(m_effectiveZoom);
 }
 
 float SVGTextLayoutEngineBaseline::calculateBaselineShift(
     const ComputedStyle& style) const {
   const SVGComputedStyle& svgStyle = style.svgStyle();
-  const SimpleFontData* fontData = m_font.primaryFont();
+  // If font size is smaller than 3, rounding ascent and descent values in
+  // SimpleFontData sets the baseline shifts for superscript and subscript to
+  // zero. In this case,  we use subpixel ascent and descent.
+  const SimpleFontData* fontData =
+      m_font.getFontDescription().getSize().value < 3.0
+          ? m_font.primaryFont()->subpixelAscentDescentFontData().get()
+          : m_font.primaryFont();
   DCHECK(fontData);
   if (!fontData)
     return 0;
 
   DCHECK(m_effectiveZoom);
   switch (svgStyle.baselineShift()) {
     case BS_LENGTH:
       return SVGLengthContext::valueForLength(
           svgStyle.baselineShiftValue(), style,
           m_font.getFontDescription().computedPixelSize() / m_effectiveZoom);
@@ skipping 108 matching lines @@
     case AB_MATHEMATICAL:
       return ascent / 2;
     case AB_BASELINE:
     default:
       ASSERT_NOT_REACHED();
       return 0;
   }
 }
 
 }  // namespace blink