Since DrawImage has grown and we've introduced PaintImage, we need to go back and make sure that it all looks good. Specifically:

- Try to eliminate DrawImage copies (down to 0 if possible)
- Figure out what is stored in a DrawImage and PaintImage and document that in cc/README.md
- Slim down DrawImage/PaintImage if possible by externalizing things that we don't need (we might need everything though).