In webkitpy-patch rebaseline-cl, don't try to rebaseline non-existent tests.

third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl.py

 # Copyright 2016 The Chromium Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
 """A command to fetch new baselines from try jobs for a Rietveld issue.
 
 This command interacts with the Rietveld API to get information about try jobs
 with layout test results.
 """
 
@@ skipping 55 matching lines @@
             # or started builds.
             _log.info('No builds to download baselines from.')
 
         if args:
             test_prefix_list = {}
             for test in args:
                 test_prefix_list[test] = {b: BASELINE_SUFFIX_LIST for b in builds}
         else:
             test_prefix_list = self._test_prefix_list(
                 issue_number, only_changed_tests=options.only_changed_tests)
+
+        # TODO(qyearsley): Fix places where non-existing tests may be added:
+        #  1. Make sure that the tests obtained when passing --only-changed-tests include only existing tests.
+        #  2. Make sure that update-w3c-test-expectations doesn't specify non-existing tests (http://crbug.com/649691).
+        test_prefix_list = self._filter_existing(test_prefix_list)
+
         self._log_test_prefix_list(test_prefix_list)
 
         if options.dry_run:
             return
         self._rebaseline(options, test_prefix_list)
 
+    def _filter_existing(self, test_prefix_list):
+        """Filters out entries in |test_prefix_list| for tests that don't exist."""
+        new_test_prefix_list = {}
+        port = self._tool.port_factory.get()
+        for test in test_prefix_list:
+            path = port.abspath_for_test(test)
+            if self._tool.filesystem.exists(path):
+                new_test_prefix_list[test] = test_prefix_list[test]
+            else:
+                _log.warning('%s not found, removing from list.', path)
+        return new_test_prefix_list
+
     def _get_issue_number(self, options):
         """Gets the Rietveld CL number from either |options| or from the current local branch."""
         if options.issue:
             return options.issue
         issue_number = self.git_cl().get_issue_number()
         _log.debug('Issue number for current branch: %s', issue_number)
         if not issue_number.isdigit():
             _log.error('No issue number given and no issue for current branch. This tool requires a CL\n'
                        'to operate on; please run `git cl upload` on this branch first, or use the --issue\n'
                        'option to download baselines for another existing CL.')
@@ skipping 78 matching lines @@
     @staticmethod
     def _log_test_prefix_list(test_prefix_list):
         """Logs the tests to download new baselines for."""
         if not test_prefix_list:
             _log.info('No tests to rebaseline; exiting.')
             return
         _log.info('Tests to rebaseline:')
         for test, builds in test_prefix_list.iteritems():
             builds_str = ', '.join(sorted('%s (%s)' % (b.builder_name, b.build_number) for b in builds))
             _log.info('  %s: %s', test, builds_str)