[Findit] Initial code of findit for crash. Add scorers to apply heuristic rules.

appengine/findit/crash/scorers/aggregator.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.
+
+"""Aggregator aggregates all the scorers passed in.
+
+Multiplies scores together and combines reasons and summaries the result.
+"""
+
+
+class Aggregator(object):
+
+  def __init__(self, scorers):
+    self.scorers = scorers
+
+  def ScoreAndReason(self, result):
+    """Sets result.confidence and result.reason."""
+
+    score = 1.0
+    reason = ''
+    for i, scorer in enumerate(self.scorers):
+      current_score, current_reason = scorer(result)
+      # TODO(katesonia): Compare this mutiply aggregator with a vector of scores
+      # aggregator later.
+      score *= current_score
+      reason += '%d. %s (score: %d)\n' % (i + 1, current_reason, current_score)
+
+    reason += '\n%s' % str(result)
+
+    result.confidence = score
+    result.reason = reason