Add lock on ASTextNode.attributedText (facebookarchive#3025)

Author: Adlai Holler

AsyncDisplayKit/ASTextNode.mm

@@ -134,6 +134,7 @@ @implementation ASTextNode {
 
   NSArray *_exclusionPaths;
 
+  NSAttributedString *_attributedText;
   NSAttributedString *_composedTruncationText;
 
   NSString *_highlightedLinkAttributeName;
@@ -368,6 +369,12 @@ + (CGFloat)ascenderWithAttributedString:(NSAttributedString *)attributedString
   return lineHeight + font.descender;
 }
 
+- (NSAttributedString *)attributedText
+{
+  ASDN::MutexLocker l(__instanceLock__);
+  return _attributedText;
+}
+
 - (void)setAttributedText:(NSAttributedString *)attributedText
 {