[Monitoring] Testcase upload metrics for the triage lifecycle

[vitorguidi]

Motivation

Chrome security shepherds manually upload testcases through appengine, triggering analyze task and, in case of a legitimate crash, the followup progression tasks:

• Minimize
• Analyze
• Impact
• Regression
• Cleanup cronjob, when updating a bug to inform the user that all above stages were finished

This PR adds instrumentation to track the time elapsed between the user upload, and the completion of the above events.

Attention points

• TestcaseUploadMetadata.timestamp was being mutated on the preprocess stage for analyze task. This mutation was removed, so that this entity can be the source of truth for when a testcase was in fact uploaded by the user.

• The job name could be retrieved from the JOB_NAME env var within the uworker, however this does not work for the cleanup use case. For this reason, the job name is fetched from datastore instead.

• The query_testcase_upload_metadata method was moved from analyze_task.py to a helpers file, so it could be reused across tasks and on the cleanup cronjob

Testing strategy

Every task mentioned was executed locally, with a valid uploaded testcase. The codepath for the metric emission was hit and produced the desired output, both for the tasks and the cronjob.

Part of #4271

[jonathanmetzman]

TestcaseUploadMetadata.timestamp was being mutated on the preprocess stage for analyze task. This mutation was removed, so that this entity can be the source of truth for when a testcase was in fact uploaded by the user.

Why was it OK to remove this?

[jonathanmetzman]

lgtm

[alhijazi]

LGTM % Jonathan's comments

[vitorguidi]

TestcaseUploadMetadata.timestamp was being mutated on the preprocess stage for analyze task. This mutation was removed, so that this entity can be the source of truth for when a testcase was in fact uploaded by the user.

Why was it OK to remove this?

The only place where this gets used is here

clusterfuzz/src/appengine/handlers/upload_testcase.py

Line 95 in 082b008

query = datastore_query.Query(data_types.TestcaseUploadMetadata)

This would only change the presentation of the uploaded testcases page in appengine, so I expect no badness from this movement.