How to display available branches in Android source tree?

The manifests are already checked out as part of the repo init process. To get a list of available branches, (from your android repo checkout root), use this command:

git --git-dir .repo/manifests/.git/ branch -a

The quickest way to list available branches without cloning/downloading anything is this one-liner:

$ git ls-remote -h https://android.googlesource.com/platform/manifest.git

It doesn't seem to be possible using the "repo" script, but you can query the list of available branches using git:

$ git clone https://android.googlesource.com/platform/manifest.git
$ cd manifest
$ git branch -r

If you don't want to clone the repository just for this, you can see the branches on the web interface.