This includes:

8bb1a22 - Use a single SharedMem rather than one per direction.

Also adds a hidden pref media.audioipc.shm_area_size (defaulting to 2MB, which was the hardcoded value in AudioIPC prior to 8bb1a22).

https://treeherder.mozilla.org/jobs?repo=try&revision=bc6bb138f1ea7990630d2f64caaff95aee0e5263

Backed out for causing failures at Mutex_posix.cpp.

Backout link: https://hg.mozilla.org/integration/autoland/rev/68f62eefce76d535b1b59805b925374c840a7e89

Push with failures: https://treeherder.mozilla.org/jobs?repo=autoland&selectedTaskRun=JEB1DmfESBWSG3i4cfGP1A.0&resultStatus=testfailed%2Cbusted%2Cexception%2Cretry%2Cusercancel&searchStr=linux%2C18.04%2Cx64%2Cwebrender%2Cdebug%2Cmochitests%2Ctest-linux1804-64-qr%2Fdebug-mochitest-devtools-chrome-e10s%2Cdt5&revision=634412ce29430557eec6d0c0313f1908e61ad13d

Failure log: https://treeherder.mozilla.org/logviewer?job_id=348008383&repo=autoland&lineNumber=8648

(In reply to Atila Butkovits from comment #3)

Backed out for causing failures at Mutex_posix.cpp.

Fix for this issue looks good on Try, but there's an unusually high number of oranges in dt and bc tests, will continue investigating.

https://hg.mozilla.org/mozilla-central/rev/f95a1c5ef0b1

Backed out 2 changesets (bug 1724141, bug 1725749) for causing crashes (bug 1730518) a=pascalc
https://hg.mozilla.org/releases/mozilla-beta/rev/747a4159c441

I am marking 94 as fixed as this backout only affected beta.