In Git.unstaged_files, handle the case when there are no changes.

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

Index: third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py b/third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py
index dc790442463defccbd0b90f9f4ab79a8fd9d93aa..1f8effd8d9d03f9957efce860a00aa0c98980d77 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/common/checkout/scm/git.py
@@ -121,9 +121,12 @@ class Git(SCM):
         """
         # `git status -z` is a version of `git status -s`, that's recommended
         # for machine parsing. Lines are terminated with NUL rather than LF.
+        change_lines = self._run_git(['status', '-z']).rstrip('\x00')
+        if not change_lines:
+            return {}  # No changes.
         unstaged_changes = {}

[qyearsley, 2016/12/28 18:47:20]

Here, if there are no changes, then change_lines is [''], and line[1] hits an
IndexError.

-        change_lines = self._run_git(['status', '-z']).rstrip('\x00').split('\x00')
-        for line in change_lines:
+        for line in change_lines.split('\x00'):
+            assert len(line) > 4, 'Unexpected change line format %s' % line
             if line[1] == ' ':
                 continue  # Already staged for commit.
             path = line[3:]