Add git cl split.

`git cl split` splits a branch into smaller branches and
uploads CLs.

Change-Id: Ic41cdabdd6241008ff48766e31a8d9d07995f2b0
Reviewed-on: https://chromium-review.googlesource.com/439706
Commit-Queue: Francois Pierre Doray <fdoray@chromium.org>
Reviewed-by: Aaron Gable <agable@chromium.org>
diff --git a/owners.py b/owners.py
index c117807..fd0c800 100644
--- a/owners.py
+++ b/owners.py
@@ -199,7 +199,7 @@
       objname = self.os_path.dirname(objname)
     return False
 
-  def _enclosing_dir_with_owners(self, objname):
+  def enclosing_dir_with_owners(self, objname):
     """Returns the innermost enclosing directory that has an OWNERS file."""
     dirpath = objname
     while not self._owners_for(dirpath):
@@ -415,7 +415,7 @@
     return owners
 
   def _covering_set_of_owners_for(self, files, author):
-    dirs_remaining = set(self._enclosing_dir_with_owners(f) for f in files)
+    dirs_remaining = set(self.enclosing_dir_with_owners(f) for f in files)
     all_possible_owners = self.all_possible_owners(dirs_remaining, author)
     suggested_owners = set()
     while dirs_remaining and all_possible_owners: