SVG doesn't recognize ch units.

Source/core/svg/SVGLengthContext.h

 /*
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 25 matching lines @@
     LengthTypeNumber,
     LengthTypePercentage,
     LengthTypeEMS,
     LengthTypeEXS,
     LengthTypePX,
     LengthTypeCM,
     LengthTypeMM,
     LengthTypeIN,
     LengthTypePT,
     LengthTypePC,
-    LengthTypeREMS
+    LengthTypeREMS,
+    LengthTypeCHS
 };
 
 enum class SVGLengthMode {
     Width,
     Height,
     Other
 };
 
 class SVGLengthContext {
     STACK_ALLOCATED();
@@ skipping 19 matching lines @@
 
     bool determineViewport(FloatSize&) const;
 
 private:
     float valueForLength(const Length&, float zoom, SVGLengthMode) const;
     static float valueForLength(const Length&, float zoom, float dimension);
 
     float convertValueFromUserUnitsToEXS(float value) const;
     float convertValueFromEXSToUserUnits(float value) const;
 
+    float convertValueFromUserUnitsToCHS(float value) const;
+    float convertValueFromCHSToUserUnits(float value) const;
+
     RawPtrWillBeMember<const SVGElement> m_context;
 };
 
 } // namespace blink
 
 #endif // SVGLengthContext_h