Bug 988877: Shut down MediaManager thread in xpcom-shutdown r=bsmedberg
Bug 1008619: Release MediaEngineWebRTC at MediaManager shutdown r=anant
Bug 891551 - Part 2: (Upliftable) Fix bugs where PR_WOULD_BLOCK_ERROR (or, in some cases, PR_NOT_CONNECTED_ERROR while a TCP socket was connecting) would cause sockets to be abandoned for no good reason (see also bug 985493 and 1001671). r=bwc