Fix missing imports on tests.
Fix missing imports on tests.

Shraddha512/rust-http,chris-morgan/rust-http,servo/rust-http,servo/rust-http,chris-morgan/rust-http,Shraddha512/rust-http,Shraddha512/rust-http,chris-morgan/rust-http,servo/rust-http,Shraddha512/rust-http,Shraddha512/rust-http,servo/rust-http,chris-morgan/rust-http