SVG doesn't recognize ch units.

Source/core/svg/SVGLengthContext.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Apple Inc. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. 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.
@@ skipping 202 matching lines @@
         break;
     case LengthTypePT:
         userUnits = value * cssPixelsPerPoint;
         break;
     case LengthTypePC:
         userUnits = value * cssPixelsPerPica;
         break;
     case LengthTypeREMS:
         userUnits = convertValueFromEMSToUserUnits(rootElementStyle(m_context), value);
         break;
+    case LengthTypeCHS:
+        userUnits = convertValueFromCHSToUserUnits(value);
+        break;
     default:
         ASSERT_NOT_REACHED();
         break;
     }
 
     // Since we mix css <length> values with svg's length values we need to
     // clamp values to the narrowest range, otherwise it can result in
     // rendering issues.
     return CSSPrimitiveValue::clampToCSSLengthRange(userUnits);
 }
@@ skipping 12 matching lines @@
         // LengthTypePercentage is represented with 100% = 100.0.
         // Good for accuracy but could eventually be changed.
         return value * 100 / dimensionForLengthMode(mode, viewportSize);
     }
     case LengthTypeEMS:
         return convertValueFromUserUnitsToEMS(computedStyleForLengthResolving(m_context), value);
     case LengthTypeEXS:
         return convertValueFromUserUnitsToEXS(value);
     case LengthTypeREMS:
         return convertValueFromUserUnitsToEMS(rootElementStyle(m_context), value);
+    case LengthTypeCHS:
+        return convertValueFromUserUnitsToCHS(value);
     case LengthTypePX:
         return value;
     case LengthTypeCM:
         return value / cssPixelsPerCentimeter;
     case LengthTypeMM:
         return value / cssPixelsPerMillimeter;
     case LengthTypeIN:
         return value / cssPixelsPerInch;
     case LengthTypePT:
         return value / cssPixelsPerPoint;
     case LengthTypePC:
         return value / cssPixelsPerPica;
     }
 
     ASSERT_NOT_REACHED();
     return 0;
 }
 
+float SVGLengthContext::convertValueFromUserUnitsToCHS(float value) const
+{
+    const ComputedStyle* style = computedStyleForLengthResolving(m_context);
+    if (!style)
+        return 0;
+
+    float zeroWidth = style->fontMetrics().zeroWidth();
+    if (!zeroWidth)
+        return 0;
+
+    return value / zeroWidth;
+}
+
+float SVGLengthContext::convertValueFromCHSToUserUnits(float value) const
+{
+    const ComputedStyle* style = computedStyleForLengthResolving(m_context);
+    if (!style)
+        return 0;
+
+    return value * style->fontMetrics().zeroWidth();
+}
+
 float SVGLengthContext::convertValueFromUserUnitsToEXS(float value) const
 {
     const ComputedStyle* style = computedStyleForLengthResolving(m_context);
     if (!style)
         return 0;
 
     // Use of ceil allows a pixel match to the W3Cs expected output of coords-units-03-b.svg
     // if this causes problems in real world cases maybe it would be best to remove this
     float xHeight = ceilf(style->fontMetrics().xHeight());
     if (!xHeight)
@@ skipping 31 matching lines @@
 
     const SVGSVGElement& svg = toSVGSVGElement(*viewportElement);
     viewportSize = svg.currentViewBoxRect().size();
     if (viewportSize.isEmpty())
         viewportSize = svg.currentViewportSize();
 
     return true;
 }
 
 }