If you use the rebaseline.py script with a .git repo,

webkit/tools/layout_tests/rebaseline.py

 #!/usr/bin/env python
 # Copyright (c) 2006-2009 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.
 
 """Rebaselining tool that automatically produces baselines for all platforms.
 
 The script does the following for each platform specified:
   1. Compile a list of tests that need rebaselining.
   2. Download test result archive from buildbot for the platform.
@@ skipping 404 matching lines @@
 
     Returns:
       True if the file already exists in SVN or is sucessfully added to SVN.
       False otherwise.
     """
 
     if not filename:
       return False
 
     parent_dir, basename = os.path.split(filename)
+    if parent_dir == filename:
+      logging.info("No svn checkout found. Assuming it's a git repo and not "
+                   "adding")
+      return True
+
     original_dir = os.getcwd()
     os.chdir(parent_dir)
     status_output = RunShell(['svn', 'status', basename], False)
     os.chdir(original_dir)
     output = status_output.upper()
     if output.startswith('A') or output.startswith('M'):
       logging.info('  File already added to SVN: "%s"', filename)
       return True
 
     if output.find('IS NOT A WORKING COPY') >= 0:
@@ skipping 375 matching lines @@
     LogDashedString('Rebaselining result comparison started', None)
     html_generator = HtmlGenerator(options, platforms, rebaselining_tests)
     html_generator.GenerateHtml()
     html_generator.ShowHtml()
     LogDashedString('Rebaselining result comparison done', None)
 
   sys.exit(0)
 
 if '__main__' == __name__:
   main()