httptrace.ContextClientTrace
// ContextClientTrace returns the ClientTrace associated with the
// provided context. If none, it returns nil.
func ContextClientTrace(ctx context.Context) *ClientTrace
httptrace.WithClientTrace
// WithClientTrace returns a new context based on the provided parent
// ctx. HTTP client requests made with the returned context will use
// the provided trace hooks, in addition to any previous hooks
// registered with ctx. Any hooks defined in the provided trace will
// be called first.
func WithClientTrace(ctx context.Context, trace *ClientTrace) context.Context