Add git subtree daemon service.

infra/libs/git2/test/ref_test.py

 # Copyright 2014 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 from infra.libs import git2
 from infra.libs.git2.test import test_util
 
 
 class TestRef(test_util.TestBasis):
   def testComparison(self):
@@ skipping 43 matching lines @@
         list(c.hsh for c in dne.to(O)),
         [self.repo[c] for c in 'ABCDLMNO']
     )
 
   def testUpdateTo(self):
     r = self.mkRepo()
     O = r['refs/heads/branch_O']
     S = r.get_commit(self.repo['S'])
     self.capture_stdio(O.update_to, S)
     self.assertEqual(O.commit.hsh, self.repo['S'])
+
+  def testHash(self):
+    # ensure that Ref's can be used as keys in a dict
+    r = self.mkRepo()
+    mapping = {}
+    mapping[r['refs/heads/branch_O']] = True
+    mapping[r['refs/heads/branch_O']] = True
+    self.assertEqual(len(mapping), 1)