Disallow [ Missing ] expectations in test expectations files.

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/models/test_expectations.py

 # Copyright (C) 2010 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 417 matching lines @@
 
         if 'NeverFixTests' in filename and expectations != ['WONTFIX', 'SKIP']:
             warnings.append('Only WONTFIX expectations are allowed in NeverFixTests')
 
         if 'SlowTests' in filename and expectations != ['SLOW']:
             warnings.append('Only SLOW expectations are allowed in SlowTests')
 
         if not expectations and not has_unrecognized_expectation:
             warnings.append('Missing expectations.')
 
+        if 'MISSING' in expectations:
+            warnings.append(
+                '"Missing" expectations are not allowed; either download new baselines '
+                '(see https://goo.gl/SHVYrZ) or use "NeedsRebaseline" expecatations.')
+
         expectation_line.bugs = bugs
         expectation_line.specifiers = specifiers
         expectation_line.expectations = expectations
         expectation_line.name = name
         expectation_line.warnings = warnings
         return expectation_line
 
     @staticmethod
     def create_passing_expectation(test):
         expectation_line = TestExpectationLine()
@@ skipping 749 matching lines @@
             # If reconstitute_only_these is an empty list, we want to return original_string.
             # So we need to compare reconstitute_only_these to None, not just check if it's falsey.
             if reconstitute_only_these is None or expectation_line in reconstitute_only_these:
                 return expectation_line.to_string(test_configuration_converter)
             return expectation_line.original_string
 
         def nones_out(expectation_line):
             return expectation_line is not None
 
         return "\n".join(filter(nones_out, map(serialize, expectation_lines)))