Creates an instance of LoadManager.
The target iframe element to manage.
Cleans up all registered message event listeners previously added by _listenForMessage.
Call this method when the instance is being destroyed or no longer needs to listen to messages.
Initializes the LoadManager by listening for a "loadState" message from the iframe. Resolves when the iframe reports that it's in a "ready" state.
A promise that resolves with 'ready' and a ready state of
Manages the loading state of an iframe and communicates with it via postMessage.