Summary:
using namespace in header file is a bad practice due to many reasons as well as discouraged by `-Wheader-hygiene` compiler flag which is default for many apps
https://stackoverflow.com/questions/5849457/using-namespace-in-c-headers
Changelog:
[General][Fixed] - Fixed compilation warning due to `using namespace` being used as part of header
Reviewed By: nlutsenko
Differential Revision: D34788523
fbshipit-source-id: 2a50fbf2ac3371ff5670c600c7f5ad9055060ad2
009d80bf5a