In Git.unstaged_files, handle the case when there are no changes.

third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/scm_unittest.py

 # Copyright (C) 2009 Google Inc. All rights reserved.
 # Copyright (C) 2009 Apple Inc. All rights reserved.
 # Copyright (C) 2011 Daniel Bates (dbates@intudata.com). All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #    * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
@@ skipping 237 matching lines @@
         self.assertEqual(scm.timestamp_of_revision('some-path', '12345'), '2013-02-08T08:05:49Z')
 
         scm._run_git = lambda args: 'Date: 2013-02-08 01:02:03 +0130'
         self.assertEqual(scm.timestamp_of_revision('some-path', '12345'), '2013-02-07T23:32:03Z')
 
         scm._run_git = lambda args: 'Date: 2013-02-08 01:55:21 -0800'
         self.assertEqual(scm.timestamp_of_revision('some-path', '12345'), '2013-02-08T09:55:21Z')
 
     def test_unstaged_files(self):
         scm = self.make_scm()
-        status_lines = [
+        lines = [
             ' M d/modified.txt',
             ' D d/deleted.txt',
             '?? d/untracked.txt',
             'D  d/deleted.txt',
             'M  d/modified-staged.txt',
             'A  d/added-staged.txt',
         ]
-        # pylint: disable=protected-access
-        scm._run_git = lambda args: '\x00'.join(status_lines) + '\x00'
+        scm._run_git = lambda _: '\x00'.join(lines) + '\x00'  # pylint: disable=protected-access
         self.assertEqual(
             scm.unstaged_changes(),
             {
                 'd/modified.txt': 'M',
                 'd/deleted.txt': 'D',
                 'd/untracked.txt': '?',
             })
+
+    def test_unstaged_files_with_no_changes(self):
+        scm = self.make_scm()
+        scm._run_git = lambda _: '\x00'  # pylint: disable=protected-access
+        self.assertEqual(scm.unstaged_changes(), {})