BUg 1741714 - Validate pipeline ids are not referenced multiple times during scene building r=gfx-reviewers,bradwerth
BUg 1741714 - Validate pipeline ids are not referenced multiple times during scene building r=gfx-reviewers,bradwerth

Add an earlier assert to try and validate the root cause of bug 1736069.

Differential Revision: https://phabricator.services.mozilla.com/D131435

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/4e11f6be34812842e4b0ab26993bb17cbdce9ff7

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