Docserver: there is only one.

chrome/common/extensions/docs/server2/patcher.py

 # Copyright 2013 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.
 
 class Patcher(object):
   def GetPatchedFiles(self, version=None):
-    ''' Returns patched files as(added_files, deleted_files, modified_files)
+    '''Returns patched files as(added_files, deleted_files, modified_files)
     from the patchset specified by |version|.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def GetVersion(self):
-    ''' Returns patch version. Returns None when nothing is patched by the
+    '''Returns patch version. Returns None when nothing is patched by the
     patcher.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
 
   def Apply(self, paths, file_system, binary, version=None):
-    ''' Apply the patch to added/modified files. Returns Future with patched
+    '''Apply the patch to added/modified files. Returns Future with patched
     data. Throws FileNotFoundError if |paths| contains deleted files.
     '''
-    raise NotImplementedError()
+    raise NotImplementedError(self.__class__)
+
+  def GetIdentity(self):
+    '''Returns a string that identifies this patch. Typically it would be the
+    codereview server's ID for this patch.
+    '''
+    raise NotImplementedError(self.__class__)