Support filling in baselines from other platforms in rebaseline-cl.

third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline.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 157 matching lines @@
                 for build, port_name in build_port_pairs:
                     yield (test, build, port_name)
 
     def __str__(self):
         if not self._test_prefix_map:
             return '<Empty TestBaselineSet>'
         return ('<TestBaselineSet with:\n  ' +
                 '\n  '.join('%s: %s, %s' % triple for triple in self._iter_combinations()) +
                 '>')
 
+    def test_prefixes(self):
+        return sorted(self._test_prefix_map)
+
+    def build_port_pairs(self, test_prefix):
+        # Return a copy in case the caller modifies the returned list.
+        return list(self._test_prefix_map[test_prefix])
+
     def add(self, test_prefix, build, port_name=None):
         """Adds an entry for baselines to download for some set of tests.
 
         Args:
             test_prefix: This can be a full test path, or directory of tests, or a path with globs.
             build: A Build object. This specifies where to fetch baselines from.
             port_name: This specifies what platform the baseline is for.
         """
         port_name = port_name or self._host.builders.port_name_for_builder_name(build.builder_name)
         self._builder_names.add(build.builder_name)
@@ skipping 572 matching lines @@
 
         test_baseline_set = TestBaselineSet(tool)
 
         for builder in builders_to_check:
             for test_prefix in args:
                 test_baseline_set.add(test_prefix, Build(builder))
 
         _log.debug('Rebaselining: %s', test_baseline_set)
 
         self.rebaseline(options, test_baseline_set)