Commerce Manager does not work when used in HTTPS-terminating load balancer setup

Description

Steps to reproduce:
1. Setup commerce site with https in an environment with a load balancer that terminates https.
2. Access the commerce site via the manager integration.

Expected:
No problem

Actual:
Commerce Manager does not work if HTTPS is used and terminated in a load balancer. The Commerce Manager site sees the request as HTTP and creates absolute links to stylesheets using that scheme. This leads to mixed content errors in browsers.

Note: related forum thread:
http://world.episerver.com/forum/developer-forum/Developer-to-developer/Thread-Container/2016/7/commerce-over-https-errors#MainRegion_PostList_UserProfile1_4_ForumLink_4