Document ANativeWindow's buffer refcounting

                int interval);

    /*

     * hook called by EGL to acquire a buffer. After this call, the buffer

     * is not locked, so its content cannot be modified.

     * this call may block if no buffers are available.

     * Hook called by EGL to acquire a buffer. After this call, the buffer

     * is not locked, so its content cannot be modified. This call may block if

     * no buffers are available.

     *

     * The window holds a reference to the buffer between dequeueBuffer and

     * either queueBuffer or cancelBuffer, so clients only need their own

     * reference if they might use the buffer after queueing or canceling it.

     * Holding a reference to a buffer after queueing or canceling it is only

     * allowed if a specific buffer count has been set.

     *

     * Returns 0 on success or -errno on error.

     */

    int     (*lockBuffer)(struct ANativeWindow* window,

                struct ANativeWindowBuffer* buffer);

    /*

    * hook called by EGL when modifications to the render buffer are done.

     * Hook called by EGL when modifications to the render buffer are done.

     * This unlocks and post the buffer.

     *

     * The window holds a reference to the buffer between dequeueBuffer and

     * either queueBuffer or cancelBuffer, so clients only need their own

     * reference if they might use the buffer after queueing or canceling it.

     * Holding a reference to a buffer after queueing or canceling it is only

     * allowed if a specific buffer count has been set.

     *

     * Buffers MUST be queued in the same order than they were dequeued.

     *

     * Returns 0 on success or -errno on error.

                int operation, ... );

    /*

     * hook used to cancel a buffer that has been dequeued.

     * Hook used to cancel a buffer that has been dequeued.

     * No synchronization is performed between dequeue() and cancel(), so

     * either external synchronization is needed, or these functions must be

     * called from the same thread.

     *

     * The window holds a reference to the buffer between dequeueBuffer and

     * either queueBuffer or cancelBuffer, so clients only need their own

     * reference if they might use the buffer after queueing or canceling it.

     * Holding a reference to a buffer after queueing or canceling it is only

     * allowed if a specific buffer count has been set.

     */

    int     (*cancelBuffer)(struct ANativeWindow* window,

                struct ANativeWindowBuffer* buffer);