Make layout test harness extensible with custom layout tests directory

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 297 matching lines @@
                 help=("Control whether tests that are flaky on the bots get ignored. "
                       "'very-flaky' == Ignore any tests that flaked more than once on the bot. "
                       "'maybe-flaky' == Ignore any tests that flaked once on the bot. "
                       "'unexpected' == Ignore any tests that had unexpected results on the bot.")),
             optparse.make_option(
                 "--iterations",
                 type="int",
                 default=1,
                 help="Number of times to run the set of tests (e.g. ABCABCABC)"),
             optparse.make_option(
+                "--layout-tests-directory",
+                help=("Path to a custom layout tests directory")),
+            optparse.make_option(
                 "--max-locked-shards",
                 type="int",
                 default=0,
                 help="Set the maximum number of locked shards"),
             optparse.make_option(
                 "--nocheck-sys-deps",
                 action="store_true",
                 default=False,
                 help="Don't check the system dependencies (themes)"),
             optparse.make_option(
@@ skipping 256 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)