make version of ts_mon compatible with appengine

infra_libs/ts_mon/helpers.py

-# Copyright 2015 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.
-
-"""Helper classes that make it easier to instrument code for monitoring."""
-
-
-class ScopedIncrementCounter(object):
-  """Increment a counter when the wrapped code exits.
-
-  The counter will be given a 'status' = 'success' or 'failure' label whose
-  value will be set to depending on whether the wrapped code threw an exception.
-
-  Example:
-
-    mycounter = Counter('foo/stuff_done')
-    with ScopedIncrementCounter(mycounter):
-      DoStuff()
-
-  To set a custom status label and status value:
-
-    mycounter = Counter('foo/http_requests')
-    with ScopedIncrementCounter(mycounter, 'response_code') as sc:
-      status = MakeHttpRequest()
-      sc.set_status(status)  # This custom status now won't be overwritten if
-                             # the code later raises an exception.
-  """
-
-  def __init__(self, counter, label='status', success_value='success',
-               failure_value='failure'):
-    self.counter = counter
-    self.label = label
-    self.success_value = success_value
-    self.failure_value = failure_value
-    self.status = None
-
-  def set_failure(self):
-    self.set_status(self.failure_value)
-
-  def set_status(self, status):
-    self.status = status
-
-  def __enter__(self):
-    self.status = None
-    return self
-
-  def __exit__(self, exc_type, exc_value, traceback):
-    if self.status is None:
-      if exc_type is None:
-        self.status = self.success_value
-      else:
-        self.status = self.failure_value
-    self.counter.increment({self.label: self.status})