Bug 1794343 - Return a formatted string if mapping fails in get_pbo. r=jrmuizel
Bug 1794343 - Return a formatted string if mapping fails in get_pbo. r=jrmuizel

Differential Revision: https://phabricator.services.mozilla.com/D158925

[ghsync] From https://hg.mozilla.org/mozilla-central/rev/27dd3d4b23cdbf527f758d114366f4efb3259400

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