Making CallStack immutable, so it can be hashable

appengine/findit/crash/changelist_classifier.py

Index: appengine/findit/crash/changelist_classifier.py
diff --git a/appengine/findit/crash/changelist_classifier.py b/appengine/findit/crash/changelist_classifier.py
index eb2abba2df226f7cd2c1ee16aadaa03c0228e2a7..f1a1d4446be7d45a6fccc438b164f2b4d6f93034 100644
--- a/appengine/findit/crash/changelist_classifier.py
+++ b/appengine/findit/crash/changelist_classifier.py
@@ -58,12 +58,12 @@ class ChangelistClassifier(namedtuple('ChangelistClassifier',
         last_good_version, first_bad_version)
 
     # Restrict analysis to just the top n frames in each callstack.
-    # TODO(wrengr): move this to be a Stacktrace method?
+    # TODO(wrengr): use CallStack.SliceFrames

[Martin Barbella, 2016/12/08 22:30:55]

Nit: end with period. Also, is there a reason not to do this in this CL? Are
there any other complications related to it?

[wrengr, 2016/12/08 23:42:37]

Done.

FWIW, most of the time when I'm making todo notes they are things I intend to
put in the current CL; it's just a note to myself so I don't forget to do it.
E.g., this one was made before I'd actually written SliceFrames :)

     stacktrace = Stacktrace([
         CallStack(stack.priority,
                   format_type=stack.format_type,
                   language_type=stack.language_type,
-                  frame_list=stack[:self.top_n_frames])
+                  frame_list=stack.frames[:self.top_n_frames])
         for stack in report.stacktrace])
 
     # We are only interested in the deps in crash stack (the callstack that