Always reserve space for error text in text fields. (#7206)
Always reserve space for error text in text fields. (#7206)

Fixes https://github.com/flutter/flutter/issues/6943
tvolkert/flutter,cbracken/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,turnidge/flutter,flutter/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,flutter/flutter,turnidge/flutter,cbracken/flutter,turnidge/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,flutter/flutter,turnidge/flutter,tvolkert/flutter,tvolkert/flutter,tvolkert/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,turnidge/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,flutter/flutter,cbracken/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,Hixie/flutter