[Findit] Moving check flake max_builds_to_look_back to config

appengine/findit/waterfall/flake/initialize_flake_pipeline.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.
 
-from datetime import datetime
-
 from google.appengine.ext import ndb
 
 from common import appengine_util
 from common import constants
 from model import analysis_status
 from model.flake.master_flake_analysis import MasterFlakeAnalysis
+from waterfall import waterfall_config
 from waterfall.flake.recursive_flake_pipeline import RecursiveFlakePipeline
 
-# TODO(lijeffrey): Move to config.
-MAX_BUILD_NUMBERS_TO_LOOK_BACK = 1000
-
 
 @ndb.transactional
 def NeedANewAnalysis(
     master_name, builder_name, build_number, step_name, test_name):
   """Checks status of analysis for the test and decides if a new one is needed.
 
   A MasterFlakeAnalysis entity for the given parameters will be created if none
   exists. When a new analysis is needed, this function will create and
   save a MasterFlakeAnalysis entity to the datastore.
 
@@ skipping 39 matching lines @@
     builder_name (str): The builder name of the failed test
     build_number (int): The build number of the failed test
     step_name (str): The name of the test suite
     test_name (str): The single test we are checking
 
   Returns:
     A MasterFlakeAnalysis instance.
   """
   if NeedANewAnalysis(
       master_name, builder_name, build_number, step_name, test_name):
+    check_flake_settings = waterfall_config.GetCheckFlakeSettings()
+    max_build_numbers_to_look_back = check_flake_settings.get(
+        'max_build_numbers_to_look_back')
     flakiness_algorithm_results_dict = {
         'flakes_in_a_row': 0,
         'stable_in_a_row': 0,
         'stabled_out': False,
         'flaked_out': False,
         'last_build_number': max(
-            0, build_number - MAX_BUILD_NUMBERS_TO_LOOK_BACK),
+            0, build_number - max_build_numbers_to_look_back),
         'lower_boundary': None,
         'upper_boundary': None,
         'lower_boundary_result': None,
         'sequential_run_index': 0
     }
     pipeline_job = RecursiveFlakePipeline(
         master_name, builder_name, build_number, step_name, test_name,
         master_build_number=build_number,
         flakiness_algorithm_results_dict=flakiness_algorithm_results_dict)
     pipeline_job.target = appengine_util.GetTargetNameForModule(
         constants.WATERFALL_BACKEND)
     pipeline_job.start(queue_name=queue_name)
   return MasterFlakeAnalysis.Get(
       master_name, builder_name, build_number, step_name, test_name)