Then shortcut

If the promise is already resolved and the handlers for the state that the promises resolves into wasn't provided, `return this` as quickly as possible. 
We'll need to confirm if this breaks the inspector.  Even if it doesn't, at the very least we'll have the wrong label which can be confusing.

`(new Promise(resolver, "Promise 1")).then(null, null, "Chained")`

will either not show the chain or show `Promise 1 -> Promise 1`