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

third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py b/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py
index 496ab1dd7975257aed38ee703f59b7cbcf167d67..882cd5a02965ff14a1c9cfac7ea7021084d1bb32 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline_unittest.py
@@ -484,6 +484,22 @@ class TestRebaselineJson(BaseTestCase):
                   '--builder', 'MOCK Win7', '--test', 'userscripts/first-test.html', '--verbose', '--results-directory', '/tmp']]
             ])
 
+    def test_unstaged_baselines(self):
+        scm = self.tool.scm()
+        scm.unstaged_changes = lambda: {
+            'third_party/WebKit/LayoutTests/x/foo-expected.txt': 'M',
+            'third_party/WebKit/LayoutTests/x/foo-expected.something': '?',
+            'third_party/WebKit/LayoutTests/x/foo-expected.png': '?',
+            'third_party/WebKit/LayoutTests/x/foo.html': 'M',
+            'docs/something.md': '?',
+        }
+        self.assertEqual(
+            self.command.unstaged_baselines(),
+            [
+                '/mock-checkout/third_party/WebKit/LayoutTests/x/foo-expected.png',
+                '/mock-checkout/third_party/WebKit/LayoutTests/x/foo-expected.txt',
+            ])
+
 
 class TestRebaselineJsonUpdatesExpectationsFiles(BaseTestCase):
     command_constructor = RebaselineJson