Revert "nav bar font styles are special, do not inherit (#12578)" (#12661)
Revert "nav bar font styles are special, do not inherit (#12578)" (#12661)

This reverts commit 964a138d80e4b0778bdb31f0d0c4d3b34d100f84.

It may (or may not) have caused a performance regression. Hard to say.
tvolkert/flutter,tvolkert/flutter,cbracken/flutter,flutter/flutter,flutter/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,Hixie/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,cbracken/flutter,flutter/flutter,Hixie/flutter,tvolkert/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,cbracken/flutter,cbracken/flutter,Hixie/flutter,Hixie/flutter,tvolkert/flutter,Hixie/flutter,tvolkert/flutter,flutter/flutter,flutter/flutter,tvolkert/flutter,flutter/flutter,tvolkert/flutter,Hixie/flutter,Hixie/flutter