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

third_party/WebKit/Tools/Scripts/webkitpy/w3c/update_w3c_test_expectations.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 class for updating layout test expectations when updating w3c tests.
 
 Specifically, this class fetches results from try bots for the current CL, and:
   1. Downloads new baseline files for any tests that can be rebaselined.
   2. Updates the generic TestExpectations file for any other failing tests.
 
@@ skipping 298 matching lines @@
             webkit_patch = self.host.filesystem.join(
                 self.finder.chromium_base(), self.finder.webkit_base(), self.finder.path_to_script('webkit-patch'))
             self.host.executive.run_command([
                 'python',
                 webkit_patch,
                 'rebaseline-cl',
                 '--verbose',
                 '--no-trigger-jobs',
                 '--only-changed-tests',
             ] + tests_to_rebaseline)
+            # NOTE(qyearsley): If rebaseline-cl is changed to stage all new files
+            # with git, then this would be unnecessary and should be removed.
+            self.host.executive.run_command(['git', 'add', '--all'])
         return tests_results
 
     def get_modified_existing_tests(self):
         """Returns a list of layout test names for layout tests that have been modified."""
         diff_output = self.host.executive.run_command(
             ['git', 'diff', 'origin/master', '--name-only', '-diff-filter=AMR'])  # Added, modified, and renamed files.
         paths_from_chromium_root = diff_output.splitlines()
         modified_tests = []
         for path in paths_from_chromium_root:
             absolute_path = self.host.filesystem.join(self.finder.chromium_base(), path)
@@ skipping 39 matching lines @@
 
         Args:
             test_path: A file path relative to the layout tests directory.
                 This might correspond to a deleted file or a non-test.
         """
         absolute_path = self.host.filesystem.join(self.finder.layout_tests_dir(), test_path)
         test_parser = TestParser(absolute_path, self.host)
         if not test_parser.test_doc:
             return False
         return test_parser.is_jstest()