We have numerous in-header using statements:

% grep -r '^using .*;' src/mongo/ | grep '\.h:'|wc -l
138

Some are basic typedefs. Some improperly import external namespace objects into mongo.

Filtering for `stdx` which needs to do this, there are just under 100 potential violations:

% grep -r '^using .;' src/mongo/ | grep '\.h:' | grep -v 'mongo/stdx/.\.h:' | less|wc -l
98