tl;dr: Chromium is Chrome minus:
1. Crash/usage reporting to Google.
2. Proprietary video format support
3. Embedded Flash implementation (which doesn't exist on mobile anyway).
4. Google API keys.
If what you care about is security auditability, that's pretty good. If you care about running only open source software, that's going to be very hard to do in the Android/Google-Play ecosystem.
yet, the main advertisement google trhows for android is "open source" "community driven" yadda yadda
we have already been baited and switched. but marketing takes a long time to dissipate...
here, i just clicked 2010 and clicked a random day for android.com
http://web.archive.org/web/20100112200506/http://www.android...
the 1st block is about the nexus one (market as open, but not on this page) and look! the second item on the page reads "Access to the entire platform source and information on how to contribute."
guess they forgot an asterix there saying that the "entire platform" means some of the platform.
Firefox for Android still supports Adobe's Flash plugin for Android.