[Predator] Add CrashData class to process raw json crash data.

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 e05976780f347125ebc8aa6686e67844ccc1caf7..3ba0a275caf08c25e70ab777e3d2bf0a635ef34b 100644
--- a/appengine/findit/crash/changelist_classifier.py
+++ b/appengine/findit/crash/changelist_classifier.py
@@ -199,7 +199,7 @@ def GetChangeLogsForFilesGroupedByDeps(regression_deps_rolls, stack_deps,
   dep_to_file_to_changelogs = defaultdict(lambda: defaultdict(list))
   reverted_cls = set()
 
-  for dep in stack_deps:
+  for dep in stack_deps or []:

[Martin Barbella, 2017/02/06 21:16:12]

At a glance it seems like it'd be cleaner to ensure that stack_deps is iterable
wherever we create it. In the event that we start using it in other places
later, we'd have to add these same kinds of checks.

[Sharu Jiang, 2017/02/10 22:07:20]

Done.

     # If a dep is not in regression range, than it cannot be the dep of
     # culprits.
     dep_roll = regression_deps_rolls.get(dep)