Thanks, I didn't knew that, It seems to be like Android model, where they open source it few weeks after public disclosure of features.
I'm pretty sure that it's the main line of development and I regularly receive new features, new bugs and new bug fixes as days passes. After some time all this goes to the chrome beta and finally in the chrome release.
I don't think that google adds tons of code 'behind' the back of the opensource repository which is then merged only a few weeks later, because I see a gradual change (aka. the phenotype of those changes) in the daily builds from the chromium repository.