Don't issue try jobs for OWNERS-only changes.

PRESUBMIT_test.py

 #!/usr/bin/env python
 # Copyright (c) 2012 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.
 
 import os
 import re
 import unittest
 
 import PRESUBMIT
@@ skipping 42 matching lines @@
   def ChangedContents(self):
     return self._changed_contents
 
   def NewContents(self):
     return self._new_contents
 
   def LocalPath(self):
     return self._local_path
 
 
+class MockChange(object):
+  def __init__(self, changed_files):
+    self._changed_files = changed_files
+
+  def LocalPaths(self):
+    return self._changed_files
+
+
 class IncludeOrderTest(unittest.TestCase):
   def testSystemHeaderOrder(self):
     scope = [(1, '#include <csystem.h>'),
              (2, '#include <cppsystem>'),
              (3, '#include "acustom.h"')]
     all_linenums = [linenum for (linenum, _) in scope]
     mock_input_api = MockInputApi()
     warnings = PRESUBMIT._CheckIncludeOrderForScope(scope, mock_input_api,
                                                     '', all_linenums)
     self.assertEqual(0, len(warnings))
@@ skipping 259 matching lines @@
 
   def testGoodFiles(self):
     mock_input_api = MockInputApi()
     mock_input_api.files = [
       MockFile('other/path/qux.h', ''),
       MockFile('other/path/qux.cc', ''),
     ]
     results = PRESUBMIT._CheckPatchFiles(mock_input_api, MockOutputApi())
     self.assertEqual(0, len(results))
 
+  def testOnlyOwnersFiles(self):
+    mock_change = MockChange([
+      'some/path/OWNERS',
+      'A\Windows\Path\OWNERS',
+    ])
+    results = PRESUBMIT.GetPreferredTrySlaves(None, mock_change)
+    self.assertEqual(0, len(results))
+
 
 if __name__ == '__main__':
   unittest.main()