Bug 1510030 - Make prepare_prim_for_render private. r=gw
Bug 1510030 - Make prepare_prim_for_render private. r=gw

Differential Revision: https://phabricator.services.mozilla.com/D63603

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/b37ce2b87ac7b02a82a9caf6c45f7a4dea6d6017

servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender,servo/webrender