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

third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_cl_unittest.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.
 
 import json
 import optparse
 
 from webkitpy.common.net.buildbot import Build
 from webkitpy.common.net.git_cl import GitCL
 from webkitpy.common.net.layout_test_results import LayoutTestResults
@@ skipping 281 matching lines @@
 
     def test_bails_when_one_build_is_missing_results(self):
         self.tool.buildbot.set_results(Build("MOCK Try Win", 5000), None)
         self.command.execute(self.command_options(issue=11112222), [], self.tool)
         self.assertLog([
             'ERROR: Failed to fetch results from '
             '"https://storage.googleapis.com/chromium-layout-test-archives/MOCK_Try_Win/5000/layout-test-results".\n'
             'Try starting a new job for MOCK Try Win by running :\n'
             '  git cl try -b MOCK Try Win\n'
         ])
+
+    def test_bails_when_there_are_unstaged_baselines(self):
+        scm = self.tool.scm()
+        scm.unstaged_changes = lambda: {'third_party/WebKit/LayoutTests/my-test-expected.txt': '?'}
+        self.command.execute(self.command_options(issue=11112222), [], self.tool)
+        self.assertLog([
+            'ERROR: Aborting: there are unstaged baselines:\n',
+            'ERROR:   /mock-checkout/third_party/WebKit/LayoutTests/my-test-expected.txt\n',
+        ])