Remove the "horizontal-bt" value from -webkit-writing-mode

third_party/WebKit/Source/core/css/CSSPrimitiveValueMappings.h

 /*
  * Copyright (C) 2007 Alexey Proskuryakov <ap@nypop.com>.
  * Copyright (C) 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2009 Jeff Schiller <codedread@gmail.com>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ skipping 2650 matching lines @@
     switch (e) {
     case TopToBottomWritingMode:
         m_value.valueID = CSSValueHorizontalTb;
         break;
     case RightToLeftWritingMode:
         m_value.valueID = CSSValueVerticalRl;
         break;
     case LeftToRightWritingMode:
         m_value.valueID = CSSValueVerticalLr;
         break;
-    case BottomToTopWritingMode:
-        m_value.valueID = CSSValueHorizontalBt;
-        break;
     }
 }
 
 template<> inline WritingMode CSSPrimitiveValue::convertTo() const
 {
     ASSERT(isValueID());
     switch (m_value.valueID) {
     case CSSValueHorizontalTb:
     case CSSValueLr:
     case CSSValueLrTb:
     case CSSValueRl:
     case CSSValueRlTb:
         return TopToBottomWritingMode;
     case CSSValueVerticalRl:
     case CSSValueTb:
     case CSSValueTbRl:
         return RightToLeftWritingMode;
     case CSSValueVerticalLr:
         return LeftToRightWritingMode;
-    case CSSValueHorizontalBt:
-        return BottomToTopWritingMode;
     default:
         break;
     }
 
     ASSERT_NOT_REACHED();
     return TopToBottomWritingMode;
 }
 
 template<> inline CSSPrimitiveValue::CSSPrimitiveValue(TextCombine e)
     : CSSValue(PrimitiveClass)
@@ skipping 1913 matching lines @@
     default:
         break;
     }
     ASSERT_NOT_REACHED();
     return ScrollSnapTypeNone;
 }
 
 } // namespace blink
 
 #endif