[LayoutNG] Fix enum values to conform to kEnumName in style guide.

third_party/WebKit/Source/core/layout/ng/ng_writing_mode.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/layout/ng/ng_writing_mode.h"
 
 #include "platform/text/WritingMode.h"
 #include "wtf/Assertions.h"
 
 namespace blink {
 
 NGWritingMode FromPlatformWritingMode(WritingMode mode) {
   switch (mode) {
     case TopToBottomWritingMode:
-      return HorizontalTopBottom;
+      return kHorizontalTopBottom;
     case RightToLeftWritingMode:
-      return VerticalRightLeft;
+      return kVerticalRightLeft;
     case LeftToRightWritingMode:
-      return VerticalLeftRight;
+      return kVerticalLeftRight;
     default:
       NOTREACHED();
-      return HorizontalTopBottom;
+      return kHorizontalTopBottom;
   }
 }
 
 }  // namespace blink