Try disabling test converter to see what changes it still makes.

third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_converter.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_converter.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_converter.py b/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_converter.py
index 356b601f591ea20694d0c9729538ab978d7572aa..3b3b500194a06181d95a76347eecea8df5e1ca81 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_converter.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/w3c/test_converter.py
@@ -42,17 +42,7 @@ def convert_for_webkit(new_path, filename, reference_support_info, host=Host()):
     Returns:
       A pair: the list of modified properties, and the modified text if the file was modified, None otherwise.
     """
-    contents = host.filesystem.read_binary_file(filename)
-    converter = _W3CTestConverter(new_path, filename, reference_support_info, host)
-    if filename.endswith('.css'):
-        return converter.add_webkit_prefix_to_unprefixed_properties(contents.decode('utf-8'))
-    else:
-        try:
-            converter.feed(contents.decode('utf-8'))
-        except UnicodeDecodeError:
-            converter.feed(contents.decode('utf-16'))
-        converter.close()
-        return converter.output()
+    pass
 
 
 class _W3CTestConverter(HTMLParser):