It is not a safe operation to clone a TrustedPromise, but it's really easy to derive Clone on the type and make it possible. We should add a test in https://dxr.mozilla.org/servo/source/tests/compiletest/plugin/compile-fail like:

fn cloneable<T: Clone>() {
}

fn main() {
    cloneable::<TrustedPromise>();
}