https://searchfox.org/mozilla-central/rev/59de675101da711520c0bb6e34a1ea2372e7ddbb/mobile/android/chrome/content/browser.js#748-751 still seems to use it and that file has geckoview-related traces in it. On the other hand, about:accounts does things like this https://searchfox.org/mozilla-central/rev/59de675101da711520c0bb6e34a1ea2372e7ddbb/mobile/android/chrome/content/aboutAccounts.js#347 ( window.docShell.rootTreeItem.domWindow.BrowserApp.getBrowserForDocument) which implies a same-process content + parent process, which I don't think ever happens in geckoview. So not sure how much of this is dead (yet), or how best to extract it.

Backed out for build bustages on chrome.ini

Backout link: https://hg.mozilla.org/integration/autoland/rev/7478ddea2ec2d45cdd0ffc6a8bfe5fa5203eb90d
Log link: https://treeherder.mozilla.org/logviewer.html#/jobs?job_id=285973762&repo=autoland&lineNumber=1293

https://hg.mozilla.org/mozilla-central/rev/00d187c3a0b0