The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/dbed67c599faf07473865727beed7cc65e5f3147

commit dbed67c599faf07473865727beed7cc65e5f3147
Author: Jeffrey Li <lijeffrey@chromium.org>
Date: Wed Sep 20 23:05:36 2017

[Findit] Flake Analyzer - Using valid field to determine whether try job results can be used to determine pass rate

1. Check a try job's report for the 'valid' flag.
2. 'valid' may be used to aid if something went wrong during the swarming task.
3. If 'valid' is false, bail out and assume an error occurred to avoid false positives when
   creating data points.
4. Store the error in the try job for later retrieval/investigation.

Bug:  765320 
Change-Id: Id338a1720cb8e2ccdc22f1e2797f1a6741cf9ec2
Reviewed-on: https://chromium-review.googlesource.com/676261
Commit-Queue: Jeffrey Li <lijeffrey@chromium.org>
Reviewed-by: Brandon Wylie <wylieb@chromium.org>
Reviewed-by: Shuotao Gao <stgao@chromium.org>

[modify] https://crrev.com/dbed67c599faf07473865727beed7cc65e5f3147/appengine/findit/waterfall/flake/process_flake_try_job_result_pipeline.py
[modify] https://crrev.com/dbed67c599faf07473865727beed7cc65e5f3147/appengine/findit/waterfall/flake/test/process_flake_try_job_result_pipeline_test.py