We saw this in a test run of test_mozLoadFrom.html. It leads to all sorts of badness. The problem is that when when streams are sharing a resource, and you close one of the streams, a block can arrive for the resource and be added to the stream after it's closed. This corrupts media cache state.
Created attachment 412754 [details] [diff] [review] fix Don't iterate through closed streams when searching from streams that are sharing a given resource ID.