Fix up accuracy of timing for keep-alive connections.
Fix up accuracy of timing for keep-alive connections.

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