SVG doesn't recognize ch units.

Source/core/svg/SVGLengthContext.cpp

Index: Source/core/svg/SVGLengthContext.cpp
diff --git a/Source/core/svg/SVGLengthContext.cpp b/Source/core/svg/SVGLengthContext.cpp
index 3bf1f9a27ad61ef7e4abb842f82c4149cb6ceb4b..cf0bff5f1f99ef2d6d1d743f716e16f60f887710 100644
--- a/Source/core/svg/SVGLengthContext.cpp
+++ b/Source/core/svg/SVGLengthContext.cpp
@@ -172,6 +172,9 @@ float SVGLengthContext::convertValueToUserUnits(float value, SVGLengthMode mode,
     case LengthTypeREMS:
         userUnits = convertValueFromREMSToUserUnits(value);
         break;
+    case LengthTypeCHS:
+        userUnits = convertValueFromCHSToUserUnits(value);
+        break;
     default:
         ASSERT_NOT_REACHED();
         break;
@@ -204,6 +207,8 @@ float SVGLengthContext::convertValueFromUserUnits(float value, SVGLengthMode mod
         return convertValueFromUserUnitsToEXS(value);
     case LengthTypeREMS:
         return convertValueFromUserUnitsToREMS(value);
+    case LengthTypeCHS:
+        return convertValueFromUserUnitsToCHS(value);
     case LengthTypePX:
         return value;
     case LengthTypeCM:
@@ -302,6 +307,28 @@ float SVGLengthContext::convertValueFromREMSToUserUnits(float value) const
     return value * style->specifiedFontSize();
 }
 
+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);