Make Headers be one sementics node in gallery (#17445)
Make Headers be one sementics node in gallery (#17445)


flutter/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter,tvolkert/flutter,cbracken/flutter,tvolkert/flutter,tvolkert/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter