With topnav, 100% iframe height doesn’t take into account the top nav height

Issue Summary

With topnav, 100% iframe height doesn’t take into account the top nav height, so they’re getting double scrollbars when rendering their Scroll Document app.

https://community.developer.atlassian.com/t/sizetoparent-general-pages-have-the-wrong-height-on-cloud/34744/2

Steps to Reproduce

1. https://community.developer.atlassian.com/t/sizetoparent-general-pages-have-the-wrong-height-on-cloud/34744/2

Expected Results

NO double scrollbars

Actual Results

The below exception is thrown in the xxxxxxx.log file:

...

Workaround

No known workaround