In update-w3c-test-expectations, stage all new files before committing.

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 65 matching lines @@
 
         # 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
+        # NOTE(qyearsley): If this is changed to stage all new files with git,
+        # e.g. if update_scm is not False, then update_w3c_test_expectations.py
+        # should be changed to not call git add --all.
         self.rebaseline(options, test_prefix_list, update_scm=False)
 
     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]
@@ skipping 92 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)