Add git-map and git-short-map to depot_tools.

git_nav_downstream.py

+#!/usr/bin/env python
+import sys
+
+from git_common import current_branch, branches, upstream, run, hash_one
+
+
+def main(argv):
+  assert len(argv) == 1, "No arguments expected"
+  upfn = upstream
+  cur = current_branch()
+  if cur == 'HEAD':
+    upfn = lambda b: hash_one(upstream(b))
+    cur = hash_one(cur)
+  downstreams = [b for b in branches() if upfn(b) == cur]
+  if not downstreams:
+    return "No downstream branches"
+  elif len(downstreams) == 1:
+    run('checkout', downstreams[0])
+  else:
+    high = len(downstreams) - 1
+    print
+    while True:
+      print "Please select a downstream branch"
+      for i, b in enumerate(downstreams):
+        print "  %d. %s" % (i, b)
+      r = raw_input("Selection (0-%d)[0]: " % high).strip() or '0'
+      if not r.isdigit() or (0 > int(r) > high):
+        print "Invalid choice."
+      else:
+        run('checkout', downstreams[int(r)])
+        break
+
+
+if __name__ == '__main__':
+  sys.exit(main(sys.argv))