In update-w3c-test-expectations, only rebaseline newly-changed tests.

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 286 matching lines @@
         tests_to_rebaseline, tests_results = self.get_tests_to_rebaseline(modified_files, tests_results)
         if tests_to_rebaseline:
             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)
         return tests_results
 
     def get_tests_to_rebaseline(self, modified_files, tests_results):
         """Returns a list of tests to download new baselines for.
 
         Creates a list of tests to rebaseline depending on the tests' platform-
         specific results. In general, this will be non-ref tests that failed
         due to a baseline mismatch (rather than crash or timeout).
 
@@ skipping 25 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()