Stream types are deprecated to describe an audio playback use case.
But they are used for volume control. This API helps the developer
go from an AudioAttributes instance used for playback, to a
stream type used to describe which volume stream type should be
used when the user presses on the volume keys.
Test: see AudioAttributes cts test
Bug 21267880
Change-Id: I2b9da5b282e8ed2342c61c14a7f59b874d0ce979
a690473348