Bug 836599 - Part 1: Make MediaStream aware of its owner graph; r=roc

We need to make sure that MediaStream doesn't assume that it belongs
to the global graph so that we can have multiple graphs coexisting.
Bug 836599 - Part 2: Make MediaInputPort aware of its owner graph; r=roc

We need to make sure that MediaStream doesn't assume that it belongs
to the global graph so that we can have multiple graphs coexisting.
Bug 836599 - Part 3: Make MediaStreamGraphThreadRunnable know about its owner graph; r=roc
Bug 836599 - Part 4: Make MediaStreamGraphStableStateRunnable know about its owner graph; r=roc
Bug 836599 - Part 5: Make MediaStreamGraphImpl::RunInStableState not assume that it's the only graph; r=roc
Bug 836599 - Part 6: Make MediaStreamGraphImpl::AppendMessage not assume that it's the only graph; r=roc