[Predator] Pass flags to callstack detector and fix nit.

appengine/findit/crash/flag_manager.py

 # Copyright 2016 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.
 
 """Module handling flags while doing stream parsing.
 
 ``ParsingFlag`` has a name, a turn_on_condition function which returns a boolean
 predicate and a boolean value. We say that a flag with the boolean value
 ``True`` is "on", and a flag with the boolean value ``False`` is "off".
 The turn_on_condition function is used to check whether a flag should be turned
@@ skipping 39 matching lines @@
     Args:
       name (str): Name of the flag.
       turn_on_condition (callable): The function takes a str line as input and
         returns a boolean value. When the flag is "off", this funtion can be
         called to check whether the flag should be turned on or not.
         Note, if the flag is "on", the return value of this function means "do
         nothing" and shouldn't affect the value of the flag.
       value (bool): Initial value of the flag.
     """
     self._name = name
-    self._turn_on_condition = turn_on_condition
+    self._turn_on_condition = turn_on_condition or (lambda _: False)
     self._value = value
 
   @property
   def name(self):
     return self._name
 
   @property
   def value(self):
     return self._value
 
   def TurnOn(self):
     self._value = True
 
   def TurnOff(self):
     self._value = False
 
   def __nonzero__(self):
     return self._value
 
   __bool__ = __nonzero__
 
   def ConditionallyTurnOn(self, line):
     """When the flag is off, turns on it if turn_on_conditions met."""
-    if (not self._value and self._turn_on_condition and
-        self._turn_on_condition(line)):
+    if not self._value and self._turn_on_condition(line):
       self.TurnOn()
 
 
 class FlagManager(object):
   """A manager to track all the registered flags.
 
   FlagManager collects and manages flags based on group names. FlagManager takes
   care of manipulating flags during the stream parsing, including evaluating
   based on the turn_on_conditions of flags, and resetting flags.
 
@@ skipping 58 matching lines @@
 
     flag.TurnOn()
 
   def TurnOff(self, flag_name):
     """Sets the instance with flag_name to False."""
     flag = self.flags.get(flag_name)
     if flag is None:
       return
 
     flag.TurnOff()