b=911777 collect cycles before getting maxChannelCount to release some cubeb streams r=padenot

--HG--
extra : transplant_source : %C3W%96%C2J%B9%B4V%9C%C0yA%10%09%7B%B2%17%D8%E0R
b=914013 tighten detection of end of buffer playback r=ehsan

--HG--
extra : transplant_source : %40%3F%5D%9A%05%87b%97%12%7BO%8A%2Ai%F38%98%F4.%DF
b=914030 update AudioNode ownership comment r=roc

--HG--
extra : transplant_source : %B2z%F7%B7%8F%0F%AB%95N%B0%82%AC%8D%917%1B%84%3D%3A%9C
b=914030 remove MediaBufferDecoder::Shutdown(), no longer necessary since bug 900711, as part of making AudioContext::Shutdown() idempotent r=ehsan

--HG--
extra : transplant_source : %A8%BB%7D%A3%A6%87NF%F3%9D.Lu%D4%15B%10%9C%DFR
b=914030 shut down an AudioDestinationNode's graph on destruction, if not already r=ehsan

This means that the graph will be shutdown properly, even if the
AudioDestinationNode is unlinked before AudioContext::Shutdown() is called.

Making MediaStreamGraph::DestroyNonRealtimeInstance() idempotent also makes
AudioContext::Shutdown() idempotent.

--HG--
extra : transplant_source : jZ%86%C5%C2n%17%EF%C2%C0y%ED%14%0E%17_dt%0C%07
b=914030 shutdown an OfflineAudioContext when it has completed r=ehsan

This is needed to remove self-references in the graph when no more processing
will take place on the graph.

--HG--
extra : transplant_source : %EC%82%A8s%3D%08%E4%FB%8C%A5%A6%28d/2%89Rz%98s
b=914030 keep a self reference on destination while offline context is rendering r=ehsan

--HG--
extra : transplant_source : %FAk%98%E7%CB%2C%C6uf%EE%F4%CFq%3D%A7%D1%D6%E9%F1%29
b=914030 don't keep alive used AudioContexts from the window r=ehsan,bz

--HG--
extra : transplant_source : %9D%94%FF%AA%92%C7%5B8%FA%C7%DD%3A%E3W%9E%BD%7F%25%5C%19