Improve run-webkit-tests error reporting when ref tests have missing images.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/controllers/single_test_runner.py

 # Copyright (C) 2011 Google 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.
 #     * Redistributions in binary form must reproduce the above
 # copyright notice, this list of conditions and the following disclaimer
@@ skipping 440 matching lines @@
         has_stderr = reference_driver_output.has_stderr() or actual_driver_output.has_stderr()
         failures = []
         failures.extend(self._handle_error(actual_driver_output))
         if failures:
             # Don't continue any more if we already have crash or timeout.
             return TestResult(self._test_name, failures, 0, has_stderr)
         failures.extend(self._handle_error(reference_driver_output, reference_filename=reference_filename))
         if failures:
             return TestResult(self._test_name, failures, 0, has_stderr, pid=actual_driver_output.pid)
 
-        if not reference_driver_output.image_hash and not actual_driver_output.image_hash:
-            failures.append(test_failures.FailureReftestNoImagesGenerated(reference_filename))
+        if not actual_driver_output.image_hash:
+            failures.append(test_failures.FailureReftestNoImageGenerated(reference_filename))
+        elif not reference_driver_output.image_hash:
+            failures.append(test_failures.FailureReftestNoReferenceImageGenerated(reference_filename))
         elif mismatch:
             if reference_driver_output.image_hash == actual_driver_output.image_hash:
                 failures.append(test_failures.FailureReftestMismatchDidNotOccur(reference_filename))
         elif reference_driver_output.image_hash != actual_driver_output.image_hash:
             diff, err_str = self._port.diff_image(reference_driver_output.image, actual_driver_output.image)
             if diff:
                 failures.append(test_failures.FailureReftestMismatch(reference_filename))
             elif err_str:
                 _log.error(err_str)
             else:
                 _log.warning("  %s -> ref test hashes didn't match but diff passed", self._test_name)
 
         return TestResult(self._test_name, failures, 0, has_stderr, pid=actual_driver_output.pid)