Fix race in buffer ref counting.

#include <media/stagefright/MetaData.h>

#include <ui/GraphicBuffer.h>

#include <sys/atomics.h>

namespace android {

// XXX make this truly atomic.

static int atomic_add(int *value, int delta) {

    int prev_value = *value;

    *value += delta;

    return prev_value;

}

MediaBuffer::MediaBuffer(void *data, size_t size)

    : mObserver(NULL),

      mNextBuffer(NULL),

        return;

    }

    int prevCount = atomic_add(&mRefCount, -1);

    int prevCount = __atomic_dec(&mRefCount);

    if (prevCount == 1) {

        if (mObserver == NULL) {

            delete this;

}

void MediaBuffer::add_ref() {

    atomic_add(&mRefCount, 1);

    (void) __atomic_inc(&mRefCount);

}

void *MediaBuffer::data() const {