Once both https://github.com/flutter/flutter/issues/17258 and https://github.com/flutter/flutter/issues/17259 are done, we should update our golden file comparators to write helpful images to the output folder. Namely: 1. Golden image 1. Recorded image 1. Diff image (where matching pixels are transparent, and differing pixels are brightly colored) 2. Optionally, a simple HTML page to visualize the diffs