Try SlimmingPaintInvalidation

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/run_webkit_tests.py

 # Copyright (C) 2010 Google Inc. All rights reserved.
 # Copyright (C) 2010 Gabor Rapcsanyi (rgabor@inf.u-szeged.hu), University of Szeged
 # Copyright (C) 2011 Apple Inc. 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 105 matching lines @@
                 "--add-platform-exceptions",
                 action="store_true",
                 default=False,
                 help=("Save generated results into the *most-specific-platform* directory rather "
                       "than the *generic-platform* directory")),
             optparse.make_option(
                 "--additional-driver-flag",
                 "--additional-drt-flag",
                 dest="additional_driver_flag",
                 action="append",
-                default=[],
+                default=['--enable-slimming-paint-invalidation'],
                 help=("Additional command line flag to pass to the driver. Specify multiple "
                       "times to add multiple flags.")),
             optparse.make_option(
                 "--additional-expectations",
                 action="append",
                 default=[],
                 help=("Path to a test_expectations file that will override previous "
                       "expectations. Specify multiple times for multiple sets of overrides.")),
             optparse.make_option(
                 "--additional-platform-directory",
@@ skipping 478 matching lines @@
             _log.debug("\t%s", process)
 
         return run_details
 
     finally:
         printer.cleanup()
 
 if __name__ == '__main__':
     exit_code = main(sys.argv[1:], sys.stdout, sys.stderr)
     sys.exit(exit_code)