Split Placeholder into InputPlaceholder and OutputPlaceholder.

recipe_modules/json/api.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.
 
 import functools
 import collections
 import contextlib
 import json
 
 from recipe_engine import recipe_api
 from recipe_engine import util as recipe_util
 from recipe_engine import config_types
 
 
-class JsonOutputPlaceholder(recipe_util.Placeholder):
+class JsonOutputPlaceholder(recipe_util.OutputPlaceholder):
   """JsonOutputPlaceholder is meant to be a placeholder object which, when added
   to a step's cmd list, will be replaced by annotated_run with the path to a
   temporary file (e.g. /tmp/tmp4lp1qM) which will exist only for the duration of
   the step. If the script requires a flag (e.g. --output-json /path/to/file),
   you must supply that flag yourself in the cmd list.
 
   This placeholder can be optionally added when you use the Steps.step()
   method in this module.
 
   FIXME
@@ skipping 92 matching lines @@
         name,
         """
         import shutil
         import sys
         shutil.copy(sys.argv[1], sys.argv[2])
         """,
         args=[path, self.output(add_json_log=add_json_log)],
         add_python_log=False,
         **kwargs
     )