Audio service provides core audio functionality. Work in progress, the tracking bug: https://crbug.com/id=792441. The design doc: https://docs.google.com/document/d/1s_Fd1WRDdpb5n6C2MSJjeC3fis6hULZwfKMeDd4K5tI/edit?usp=sharing. TODO(olka, maxmorin, dalecurtis): Write a longer document.