Bug 1376303 - Expose aria-orientation via NSAccessibilityOrientationAttribute. r=MarcoZ

Add orientation() method to the macOS accessibility wrapper, mapping
states::Horizontal to NSAccessibilityHorizontalOrientationValue,
states::NSAccessibilityVerticalOrientationValue and the absence of
both to NSAccessibilityUnknownOrientationValue.

accessible/mac/mozAccessible.h

@@ -114,6 +114,9 @@ static const uintptr_t IS_PROXY = 1;
 // the accessible description (help text) of this particular instance.
 - (NSString*)help;
 
+// returns the orientation (vertical, horizontal, or undefined)
+- (NSString*)orientation;
+
 - (BOOL)isEnabled;
 
 // information about focus.

accessible/mac/mozAccessible.mm

@@ -323,6 +323,9 @@ ConvertToNSArray(nsTArray<ProxyAccessible*>& aArray)
   }
   if ([attribute isEqualToString:NSAccessibilityHelpAttribute])
     return [self help];
+  if ([attribute isEqualToString:NSAccessibilityOrientationAttribute])
+    return [self orientation];
+
   if ([attribute isEqualToString:NSAccessibilityDOMIdentifierAttribute]) {
     nsAutoString id;
     if (accWrap)
@@ -1067,6 +1070,28 @@ struct RoleDescrComparator
   NS_OBJC_END_TRY_ABORT_BLOCK_NIL;
 }
 
+- (NSString*)orientation
+{
+  NS_OBJC_BEGIN_TRY_ABORT_BLOCK_NIL;
+
+  uint64_t state;
+  if (AccessibleWrap* accWrap = [self getGeckoAccessible])
+    state = accWrap->InteractiveState();
+  else if (ProxyAccessible* proxy = [self getProxyAccessible])
+    state = proxy->State();
+  else
+    state = 0;
+
+  if (state & states::HORIZONTAL)
+    return NSAccessibilityHorizontalOrientationValue;
+  if (state & states::VERTICAL)
+    return NSAccessibilityVerticalOrientationValue;
+
+  return NSAccessibilityUnknownOrientationValue;
+
+  NS_OBJC_END_TRY_ABORT_BLOCK_NIL;
+}
+
 // objc-style description (from NSObject); not to be confused with the accessible description above.
 - (NSString*)description
 {