Take care of this culprit.py code coverage in this cl https://codereview.chromium.org/2449853012/, as well as some bug fixing.

Is there any significant classes that don't have 100% coverage?

Ideally, we should clean up all the "pragma: no cover" in the code base, although I'm OK with occasional occurrences for some obvious & non-critical edge cases.

@stgao: It's tricky to really say for sure. The problem is that some of the unittests got moved to different files. Because of the unreliable way that coverage is computed, many things come up as "not covered" when they are in fact covered by the complete test suite (just not by the specific foo_test.py file).

Prime examples of this include: ./crash/crash_pipeline.py, ./crash/predator.py, ./crash/culprit.py, ./crash/findit.py, ./crash/component.py

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra.git/+/e50200467b7e522a03b2d9d73d6cd27d0b49874c

commit e50200467b7e522a03b2d9d73d6cd27d0b49874c
Author: katesonia <katesonia@chromium.org>
Date: Wed Nov 02 03:08:19 2016

[Predator] Fix bug in min_distance after refactor and add back skip added/deleted deps.

Also added culprit_test for culprit.py

BUG= 660621 ,  659346 

Review-Url: https://codereview.chromium.org/2449853012

[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/changelist_classifier.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/culprit.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/scorers/min_distance.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/scorers/test/aggregated_scorer_test.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/scorers/test/min_distance_test.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/test/changelist_classifier_test.py
[add] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/test/culprit_test.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/crash/test/findit_for_chromecrash_test.py
[modify] https://crrev.com/e50200467b7e522a03b2d9d73d6cd27d0b49874c/appengine/findit/model/crash/crash_analysis.py

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/297fed57bf4cb6ba3a0a6581366b80b282b6003c

commit 297fed57bf4cb6ba3a0a6581366b80b282b6003c
Author: Sharu Jiang <katesonia@google.com>
Date: Thu Jul 27 21:56:53 2017

[Predator] Add unittests to improve code coverage.

Bug:  659346 
Change-Id: I0341ea9d393761f6c53a99a4e43f98183bfbc8e5
Reviewed-on: https://chromium-review.googlesource.com/589824
Reviewed-by: Roberto Carrillo <robertocn@chromium.org>

[modify] https://crrev.com/297fed57bf4cb6ba3a0a6581366b80b282b6003c/appengine/predator/app/common/test/crash_pipeline_test.py
[modify] https://crrev.com/297fed57bf4cb6ba3a0a6581366b80b282b6003c/appengine/predator/app/common/crash_pipeline.py