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

third_party/WebKit/LayoutTests/fast/repaint/overflow-flipped-writing-mode-table-expected.txt

 {
   "bounds": [800, 600],
   "children": [
     {
       "bounds": [800, 600],
       "contentsOpaque": true,
       "drawsContent": true,
       "repaintRects": [
-        [8, 8, 100, 50]
+        [-92, 108, 50, 100]
       ],
       "paintInvalidationClients": [
         "LayoutBlockFlow DIV id='target'"
       ]
     }
   ]
 }