Vignetting Control or peripheral illumination (described by Canon) is a phenomenon of a gradual fall-off of light reaching the sensor caused by a typical converged lens design, hence resulting in a slightly darkened edge impression on the final image that was taken.
As far as the Nikon D90 is concerned, it is claimed by many that it has a built-in vignetting control feature but not explicitly stated clearly in the official Nikon web site. Pictures taken so far with my Nikon D90 has proven to be vignette-free to my naked eye. But fret not if otherwise as software like Nikon Capture NX can perform similar correction via some complicated software algorithm.
Chromatic aberration is but the imperfect single point of light spectrum convergence caused by the different refractive index of the lens to each light ray spectrum spreading from Red to Blue light waves entering the camera. More advanced Nikkor lens feature Aspherical lens technology that greatly minimizes this problem, resulting in sharper precise placement of light spectrum on each pixel point of the image taken. Again, several credible web sites claimed its built-in in the Nikon D90 and provides a detailed comparison to prove it. I could not find these information on the Nikon web site too.