https://chrome-internal.googlesource.com/chrome/theme/google_chrome/+/master has "Beta" and "Dev" badged icons for Chrome. However, for the Mac, in https://chrome-internal.googlesource.com/chrome/theme/google_chrome/+/master/mac/, there are only Stable and Canary icons. We need Beta and Dev badged icns files.

See bug 519594 for the magic that Mark did to get the current icon set perfect. I'm still trying to understand the tools he used; they're not quite documented.