Currently V4L2VideoDecodeAccelerator has a V4L2Device instance, which is stored in |image_processor_device_| member variable, designed for V4L2ImageProcessor to use. And it is used before V4L2ImageProcessor is created so we cannot create an V4L2Device instance in V4L2ImageProcessor factory method. Instead V4L2ImageProcessor has to obtain V4L2Device instance from its caller.

To make V4L2VideoDecodeAccelerator use platform agnostic method, ImageProcessorFactory::Create(), to obtain image processor, we shall remove |image_processor_device_| from V4L2VideoDecodeAccelerator.