Abort git tools if git repo has too many local branches.

tests/git_common_test.py

 #!/usr/bin/env python
 # Copyright 2013 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.
 
 """Unit tests for git_common.py"""
 
 import binascii
 import collections
 import os
@@ skipping 374 matching lines @@
   COMMIT_L = {'file': {'data': 'L'}}
 
   def setUp(self):
     super(GitMutableStructuredTest, self).setUp()
     self.repo.git('branch', '--set-upstream-to', 'root_X', 'branch_Z')
     self.repo.git('branch', '--set-upstream-to', 'branch_G', 'branch_K')
     self.repo.git('branch', '--set-upstream-to', 'branch_K', 'branch_L')
     self.repo.git('branch', '--set-upstream-to', 'root_A', 'branch_G')
     self.repo.git('branch', '--set-upstream-to', 'root_X', 'root_A')
 
+  def testTooManyBranches(self):
+    for i in xrange(30):
+      self.repo.git('branch', 'a'*i)
+
+    with self.assertRaises(SystemExit):
+      self.repo.run(list, self.gc.branches())
+
+    self.repo.git('config', 'depot-tools.branch-limit', 'cat')
+
+    with self.assertRaises(SystemExit):
+      self.repo.run(list, self.gc.branches())
+
+    self.repo.git('config', 'depot-tools.branch-limit', '100')
+
+    # should not raise
+    self.assertEqual(36, len(self.repo.run(list, self.gc.branches())))
+
   def testMergeBase(self):
     self.repo.git('checkout', 'branch_K')
 
     self.assertEqual(
       self.repo['B'],
       self.repo.run(self.gc.get_or_create_merge_base, 'branch_K', 'branch_G')
     )
 
     self.assertEqual(
       self.repo['J'],
@@ skipping 207 matching lines @@
 
       self.assertEquals(self.repo.git('status', '--porcelain').stdout, STATUS_1)
 
     self.repo.run(inner)
 
 
 if __name__ == '__main__':
   sys.exit(coverage_utils.covered_main(
     os.path.join(DEPOT_TOOLS_ROOT, 'git_common.py')
   ))