Improve documentation of setOnFrameAvailableListener.

import java.lang.ref.WeakReference;

import android.annotation.Nullable;

import android.os.Handler;

import android.os.Looper;

import android.os.Message;

     * Register a callback to be invoked when a new image frame becomes available to the

     * SurfaceTexture.

     * <p>

     * This callback may be called on an arbitrary thread, so it is not

     * The callback may be called on an arbitrary thread, so it is not

     * safe to call {@link #updateTexImage} without first binding the OpenGL ES context to the

     * thread invoking the callback.

     * </p>

     *

     * @param listener The listener to set.

     * @param listener The listener to use, or null to remove the listener.

     */

    public void setOnFrameAvailableListener(OnFrameAvailableListener listener) {

    public void setOnFrameAvailableListener(@Nullable OnFrameAvailableListener listener) {

        setOnFrameAvailableListener(listener, null);

    }

     * Register a callback to be invoked when a new image frame becomes available to the

     * SurfaceTexture.

     * <p>

     * If no handler is specified, then this callback may be called on an arbitrary thread,

     * If a handler is specified, the callback will be invoked on that handler's thread.

     * If no handler is specified, then the callback may be called on an arbitrary thread,

     * so it is not safe to call {@link #updateTexImage} without first binding the OpenGL ES

     * context to the thread invoking the callback.

     * </p>

     *

     * @param listener The listener to set.

     * @param listener The listener to use, or null to remove the listener.

     * @param handler The handler on which the listener should be invoked, or null

     * to use an arbitrary thread.

     */

    public void setOnFrameAvailableListener(final OnFrameAvailableListener listener,

            Handler handler) {

    public void setOnFrameAvailableListener(@Nullable final OnFrameAvailableListener listener,

            @Nullable Handler handler) {

        if (listener != null) {

            // Although we claim the thread is arbitrary, earlier implementation would

            // prefer to send the callback on the creating looper or the main looper