http://docs.opencv.org/2.4/doc/tutorials/introduction/android_binary_package/O4A_SDK.html is out of date.
These look more up to date:
http://answers.opencv.org/question/14546/how-to-work-with-opencv4android-in-android-studio/
https://medium.com/@sukritipaul005/a-beginners-guide-to-installing-opencv-android-in-android-studio-ea46a7b4f2d3