In rebaseline-cl, trigger try jobs with builder per invocation of git cl try.

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 87 matching lines @@
     def trigger_jobs_for_missing_builds(self, builds):
         builders_with_builds = {b.builder_name for b in builds}
         builders_without_builds = set(self._try_bots()) - builders_with_builds
         if not builders_without_builds:
             return
 
         _log.info('Triggering try jobs for:')
         for builder in sorted(builders_without_builds):
             _log.info('  %s', builder)
 
-        git_cl = GitCL(self._tool.executive)
-        command = ['try']
+        # If the builders may be under different masters, then they cannot
+        # all be started in one invocation of git cl try without providing
+        # master names. Doing separate invocations is slower, but always works
+        # even when there are builders under different master names.
         for builder in sorted(builders_without_builds):
-            command += ['-b', builder]
-        self.git_cl().run(command)
+            self.git_cl().run(['try', '-b', builder])
 
     def _test_prefix_list(self, issue_number, only_changed_tests):
         """Returns a collection of test, builder and file extensions to get new baselines for.
 
         Args:
             issue_number: The CL number of the change which needs new baselines.
             only_changed_tests: Whether to only include baselines for tests that
                are changed in this CL. If False, all new baselines for failing
                tests will be downloaded, even for tests that were not modified.
 
@@ skipping 45 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)