Add a useful error message for run-webkit-tests broken --target handling.

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 42 matching lines @@
     if options.platform and 'test' in options.platform and not 'browser_test' in options.platform:
         # It's a bit lame to import mocks into real code, but this allows the user
         # to run tests against the test platform interactively, which is useful for
         # debugging test failures.
         from webkitpy.common.host_mock import MockHost
         host = MockHost()
     else:
         host = Host()
 
     try:
+        # TODO: crbug.com/539509 - Drop this check and make --target work properly.
+        if options.configuration not in (None, 'Debug', 'Release', 'Debug_x64', 'Release_x64'):
+            raise NotImplementedError('--target must be either "Debug" or "Release"; other values do not work\n.'
+                                      'Use multiple //out directories for multiple builds if necessary.\n'
+                                      'See crbug.com/539509.')
+
         port = host.port_factory.get(options.platform, options)
     except NotImplementedError, e:
         # FIXME: is this the best way to handle unsupported port names?
         print >> stderr, str(e)
         return test_run_results.UNEXPECTED_ERROR_EXIT_STATUS
 
     try:
         return run(port, options, args, stderr, stdout).exit_code
 
     # We need to still handle KeyboardInterrupt, atleast for webkitpy unittest cases.
@@ skipping 330 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)