The stream volume was handled the same way for all different stream,
the only potential difference between each of them being the number
of steps available to the user to change the volume. This was
mapped to 99 steps of 0.5dB amplitude, offering a maximum attenuation
of -49.5dB.
This change consists in defining for each stream a curve with two
knees (3 segments) for conversion from volume index to attenuation.
This curve is defined in the AudioPolicyManager in
initializeVolumeCurves(), and can therefore be overridden by the
platform.
Note that this change doesn't modify the volume curves: this CL
enables the curves to be changed by overriding this default
behavior.
Change-Id: I575b66799c52df2906db248943b15120b8a79ea2
3aab0583d9