Add GetModifiedFiles() function to git_utils.

py/utils/git_utils.py

Index: py/utils/git_utils.py
diff --git a/py/utils/git_utils.py b/py/utils/git_utils.py
index fec79d7b6cd11f693950ab6dd1d95d660a03d350..e0bb6e06ec4f9107219da6eb0eb7dd37f913d6ae 100644
--- a/py/utils/git_utils.py
+++ b/py/utils/git_utils.py
@@ -89,6 +89,12 @@ def GetRemoteMasterHash(git_url):
                           'refs/heads/master']).rstrip()
 
 
+def GetModifiedFiles():
+  """Returns a list of locally modified files within the current working dir.
+  """
+  return shell_utils.run([GIT, 'ls-files', '-m']).splitlines()
+
+
 def GetCurrentBranch():
   return shell_utils.run([GIT, 'rev-parse', '--abbrev-ref', 'HEAD']).rstrip()