Add post_process argument to Checkout.apply_patch().

patch.py

 # coding=utf8
 # Copyright (c) 2011 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.
 """Utility functions to handle patches."""
 
 import posixpath
 import os
 import re
 
@@ skipping 255 matching lines @@
       # 'diff' header. That the only remaining invariant.
       if not self.filename in self.diff_header:
         self._fail('Diff seems corrupted.')
 
 
 class PatchSet(object):
   """A list of FilePatch* objects."""
 
   def __init__(self, patches):
     self.patches = patches
+    for p in self.patches:
+      assert isinstance(p, FilePatchBase)
 
   def set_relpath(self, relpath):
     """Used to offset the patch into a subdirectory."""
     for patch in self.patches:
       patch.set_relpath(relpath)
 
   def __iter__(self):
     for patch in self.patches:
       yield patch
 
   @property
   def filenames(self):
     return [p.filename for p in self.patches]