Bug 1072780: patch 1 - clean up CurrentDriver() use off-MSG-thread; fix InCallback() r=roc
Bug 1072775: Additional assertions for MediaStreamGraph/GraphDriver r=roc
bug 1072780: patch 3 - Fix up Revive() to not trigger assertions, and also to avoid Init() (blocking) on MainThread r=roc
bug 1072780: patch 4 - Use atomics for EnsureNextIteration to close races around CurrentDriver r=roc