Updated the MaterialBanner example, NNBD, etc (#72477)
Updated the MaterialBanner example, NNBD, etc (#72477)


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