The svn branch heuristic does roughly the same thing git-svn does: We first iterate backwards over the history to find the svn URL (like svn://svn.chromium.org/chrome/trunk/src). Then we go through all defined svn-remote section looking for one where the URL is the root of the svn URL (svn://svn.chromium.org/chrome in that case), and the fetch spec looks like "trunk/src:remotes/origin/trunk". If the base URL + left part (trunk/src) is the full URL, the right part (remotes/origin/trunk) is the git ref that is updated when we do a `git svn fetch`! This works for git-svn branches that fetch from trunk as well as milestone branches.

BUG=none
TEST=none

Review URL: http://codereview.chromium.org/6597004

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@76364 0039d316-1c4b-4281-b951-d872f2087c98