Making CallStack immutable, so it can be hashable

appengine/findit/crash/component_classifier.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 collections import namedtuple
 from collections import defaultdict
 import logging
 import re
 
 from crash.component import Component
@@ skipping 60 matching lines @@
       crash_stack (CallStack): The callstack that caused the crash.
 
     Returns:
       List of top 2 components.
     """
     # If ``results`` are available, we use the components from there since
     # they're more reliable than the ones from the ``crash_stack``.
     if results:
       classes = map(self.GetClassFromResult, results[:self.top_n])
     else:
-      classes = map(self.GetClassFromStackFrame, crash_stack[:self.top_n])
+      classes = map(self.GetClassFromStackFrame,
+          crash_stack.frames[:self.top_n])
 
     return RankByOccurrence(classes, 2)
 
   # TODO(ymzhang): use component of new path as default. RENAME might
   # need to return two (old path new path may have different components)
   def GetClassFromFileChangeInfo(self, file_change_info):
     """Determine which component is responsible for a touched file."""
     if not file_change_info:
       return None
 
@@ skipping 15 matching lines @@
        top_n: number of components assigned to this change log, default is 2
 
      Returns:
        List of components
      """
     if not change_log:
       return None
 
     classes = map(self.GetClassFromFileChangeInfo, change_log.touched_files)
     return RankByOccurrence(classes, top_n, rank_function=lambda x:-len(x))