Update AudioTrack constructor and set() comments

    public:

        // FIXME use m prefix

        size_t      frameCount;     // number of sample frames corresponding to size;

                                    // on input to obtainBuffer() it is the number of frames desired,

                                    // on input to obtainBuffer() it is the number of frames desired

                                    // on output from obtainBuffer() it is the number of available

                                    //    frames to be read

                                    // on input to releaseBuffer() it is currently ignored

    /* Creates an AudioTrack object and registers it with AudioFlinger.

     * Once created, the track needs to be started before it can be used.

     * Unspecified values are set to appropriate default values.

     * With this constructor, the track is configured for streaming mode.

     * Data to be rendered is supplied by write() or by the callback EVENT_MORE_DATA.

     * Intermixing a combination of write() and non-ignored EVENT_MORE_DATA is not allowed.

     *

     * Parameters:

     *

     *                     configuration.  Zero means to use a default value.

     * flags:              See comments on audio_output_flags_t in <system/audio.h>.

     * cbf:                Callback function. If not null, this function is called periodically

     *                     to provide new data and inform of marker, position updates, etc.

     *                     to provide new data in TRANSFER_CALLBACK mode

     *                     and inform of marker, position updates, etc.

     * user:               Context for use by the callback receiver.

     * notificationFrames: The callback function is called each time notificationFrames PCM

     *                     frames have been consumed from track input buffer.

     *                     This is expressed in units of frames at the initial source sample rate.

     * sessionId:          Specific session ID, or zero to use default.

     * transferType:       How data is transferred to AudioTrack.

     * offloadInfo:        If not NULL, provides offload parameters for

     *                     AudioSystem::getOutputForAttr().

     * uid:                User ID of the app which initially requested this AudioTrack

     *                     for power management tracking, or -1 for current user ID.

     * pid:                Process ID of the app which initially requested this AudioTrack

     *                     for power management tracking, or -1 for current process ID.

     * pAttributes:        If not NULL, supersedes streamType for use case selection.

     * threadCanCallJava:  Not present in parameter list, and so is fixed at false.

     */

    /* Creates an audio track and registers it with AudioFlinger.

     * With this constructor, the track is configured for static buffer mode.

     * Data to be rendered is passed in a shared memory buffer

     * identified by the argument sharedBuffer, which must be non-0.

     * identified by the argument sharedBuffer, which should be non-0.

     * If sharedBuffer is zero, this constructor is equivalent to the previous constructor

     * but without the ability to specify a non-zero value for the frameCount parameter.

     * The memory should be initialized to the desired data before calling start().

     * The write() method is not supported in this case.

     * It is recommended to pass a callback function to be notified of playback end by an