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

third_party/WebKit/Source/platform/text/WritingMode.h

 /*
  * Copyright (c) 2012, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 16 matching lines @@
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 #ifndef WritingMode_h
 #define WritingMode_h
 
 namespace blink {
 
 enum WritingMode {
-    TopToBottomWritingMode, RightToLeftWritingMode, LeftToRightWritingMode, BottomToTopWritingMode
+    TopToBottomWritingMode, RightToLeftWritingMode, LeftToRightWritingMode
 };
 
-// Lines have horizontal orientation; modes horizontal-tb or horizontal-bt.
+// Lines have horizontal orientation; modes horizontal-tb.
 inline bool isHorizontalWritingMode(WritingMode writingMode)
 {
-    return writingMode == TopToBottomWritingMode || writingMode == BottomToTopWritingMode;
+    return writingMode == TopToBottomWritingMode;
 }
 
-// Bottom of the line occurs earlier in the block; modes vertical-lr or horizontal-bt.
+// Bottom of the line occurs earlier in the block; modes vertical-lr.
 inline bool isFlippedLinesWritingMode(WritingMode writingMode)
 {
-    return writingMode == LeftToRightWritingMode || writingMode == BottomToTopWritingMode;
+    return writingMode == LeftToRightWritingMode;
 }
 
-// Block progression increases in the opposite direction to normal; modes vertical-rl or horizontal-bt.
+// Block progression increases in the opposite direction to normal; modes vertical-rl.
 inline bool isFlippedBlocksWritingMode(WritingMode writingMode)
 {
-    return writingMode == RightToLeftWritingMode || writingMode == BottomToTopWritingMode;
+    return writingMode == RightToLeftWritingMode;
 }
 
 } // namespace blink
 
 #endif // WritingMode_h