Introduce new API orientation() to expose aria-orientation correctly.

public/web/WebAXEnums.h

 /*
  * Copyright (C) 2013 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 231 matching lines @@
 
 // Attribute definition values.
 // These values must match blink::AccessibilityOptionalBool values.
 // Enforced in AssertMatchingEnums.cpp.
 enum WebAXOptionalBool {
     WebAXOptionalBoolUndefined = 0,
     WebAXOptionalBoolTrue,
     WebAXOptionalBoolFalse
 };
 
+// These values must match blink::AccessibilityOrientation values.
+// Enforced in AssertMatchingEnums.cpp.
+enum WebAXOrientation {
+    WebAXOrientationUndefined = 0,
+    WebAXOrientationVertical,
+    WebAXOrientationHorizontal,
+};
+
 } // namespace blink
 
 #endif