Only add unstaged baseline changes to the git index when rebaselining.

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 34 matching lines @@
             optparse.make_option(
                 '--no-trigger-jobs', dest='trigger_jobs', action='store_false', default=True,
                 help='Do not trigger any try jobs.'),
             self.no_optimize_option,
             self.results_directory_option,
         ])
         self.rietveld = Rietveld(Web())
 
     def execute(self, options, args, tool):
         self._tool = tool
+
+        unstaged_baselines = self.unstaged_baselines()
+        if unstaged_baselines:
+            _log.error('Aborting: there are unstaged baselines:')
+            for path in unstaged_baselines:
+                _log.error('  %s', path)
+            return
+
         issue_number = self._get_issue_number(options)
         if not issue_number:
             return
 
+        # TODO(qyearsley): Replace this with git cl try-results to remove
+        # dependency on Rietveld. See crbug.com/671684.
         builds = self.rietveld.latest_try_jobs(issue_number, self._try_bots())
 
         if options.trigger_jobs:
             if self.trigger_jobs_for_missing_builds(builds):
                 _log.info('Please re-run webkit-patch rebaseline-cl once all pending try jobs have finished.')
                 return
         if not builds:
             _log.info('No builds to download baselines from.')
 
         _log.debug('Getting results for Rietveld issue %d.', issue_number)
@@ skipping 158 matching lines @@
     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.debug('Tests to rebaseline:')
         for test, builds in test_prefix_list.iteritems():
             _log.debug('  %s:', test)
             for build in sorted(builds):
                 _log.debug('    %s', build)