Parse ELNG box in MP4 container

media/formats/mp4/box_definitions.h

Index: media/formats/mp4/box_definitions.h
diff --git a/media/formats/mp4/box_definitions.h b/media/formats/mp4/box_definitions.h
index b2566764aa9484289dbd86d8ab0aa1cd9747d719..d14864264664839eaf48e2b4defbf2fcd6347c2e 100644
--- a/media/formats/mp4/box_definitions.h
+++ b/media/formats/mp4/box_definitions.h
@@ -315,6 +315,11 @@ struct MEDIA_EXPORT MediaHeader : Box {
   uint16_t language_code;
 };
 
+struct MEDIA_EXPORT ExtendedLanguageTag : Box {
+  DECLARE_BOX_METHODS(ExtendedLanguageTag);
+  std::string language_tag;
+};
+
 struct MEDIA_EXPORT MediaInformation : Box {
   DECLARE_BOX_METHODS(MediaInformation);
 
@@ -326,6 +331,7 @@ struct MEDIA_EXPORT Media : Box {
 
   MediaHeader header;
   HandlerReference handler;
+  ExtendedLanguageTag extended_language_tag;
   MediaInformation information;
 };