An AudioContext can now be explicitly closed, thereby releasing any hardware resources associated with the AudioContext. Without this, developers had to depend on garbage collection of the AudioContext to release hardware resources.
Docs: http://webaudio.github.io/web-audio-api/#widl-AudioContext-close-Promise; https://developer.mozilla.org/en-US/docs/Web/API/AudioContext/close
Samples: https://github.com/GoogleChrome/samples/tree/gh-pages/webaudio-audiocontext-close