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

webkit/tools/layout_tests/rebaseline.py

Index: webkit/tools/layout_tests/rebaseline.py
diff --git a/webkit/tools/layout_tests/rebaseline.py b/webkit/tools/layout_tests/rebaseline.py
index 652c3505938a2aa083eeff9640d4146fa38b6373..2261933197d436252c2c55ff7577fd76abf2c306 100644
--- a/webkit/tools/layout_tests/rebaseline.py
+++ b/webkit/tools/layout_tests/rebaseline.py
@@ -422,6 +422,11 @@ class Rebaseliner(object):
       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)