Bind window.parent to postMessage
Bind window.parent to postMessage

The recipient's origin would be the origin of the iframe itself because
in assigning to the 'postMessage' const variable, the context of calling
the function on 'window.parent' would be lost and it would default to
window instead. Good ol' this keyword bug.

CP-2489

ProtonMail/WebClient,ProtonMail/WebClient,ProtonMail/WebClient