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

third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py

 # Copyright (c) 2009, 2010, 2011 Google Inc. All rights reserved.
 # Copyright (c) 2009 Apple Inc. All rights reserved.
 #
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 # notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
@@ skipping 94 matching lines @@
             command.extend(['--', pathspec])
         return self._run_git(command) != ''
 
     def _discard_working_directory_changes(self):
         # Could run git clean here too, but that wouldn't match subversion
         self._run_git(['reset', 'HEAD', '--hard'])
         # Aborting rebase even though this does not match subversion
         if self._rebase_in_progress():
             self._run_git(['rebase', '--abort'])
 
+    def unstaged_changes(self):
+        """Lists files with unstaged changes, including untracked files.
+
+        Returns a dict mapping modified file paths (relative to checkout root)
+        to one-character codes identifying the change, e.g. 'M' for modified,
+        'D' for deleted, '?' for untracked.
+        """
+        # `git status -z` is a version of `git status -s`, that's recommended
+        # for machine parsing. Lines are terminated with NUL rather than LF.
+        unstaged_changes = {}
+        change_lines = self._run_git(['status', '-z']).rstrip('\x00').split('\x00')
+        for line in change_lines:
+            if line[1] == ' ':
+                continue  # Already staged for commit.
+            path = line[3:]
+            unstaged_changes[path] = line[1]
+        return unstaged_changes
+
     def status_command(self):
         # git status returns non-zero when there are changes, so we use git diff name --name-status HEAD instead.
         # No file contents printed, thus utf-8 autodecoding in self.run is fine.
         return [self.executable_name, "diff", "--name-status", "--no-renames", "HEAD"]
 
     def _status_regexp(self, expected_types):
         return '^(?P<status>[%s])\t(?P<filename>.+)$' % expected_types
 
     def add_all(self, pathspec=None):
         command = ['add', '--all']
@@ skipping 205 matching lines @@
         if self.current_branch() != self._branch_tracking_remote_master():
             return False
         if len(self._local_commits(self._branch_tracking_remote_master())) > 0:
             return False
         return True
 
     def ensure_cleanly_tracking_remote_master(self):
         self._discard_working_directory_changes()
         self._run_git(['checkout', '-q', self._branch_tracking_remote_master()])
         self._discard_local_commits()