Here's the controls you have inside an iframe in Canvas based on the code here: https://github.com/instructure/canvas-lms/blob/master/public/javascripts/lti/messages.js#L74-L170
Updated w/ help from https://github.com/bagofarms after he realized my original information was incorrect. He found some readme docs from Bracken on the subject which opened things up: https://github.com/bracken/lti_messaging
const message = {
subject: 'lti.frameResize',