We should also investigate if other metric infrastructures have similar issues.

This could happen naturally if the client fails to see the collector gets the message, but the 200 response was lost.  There is no way to completely eliminate that issue.

However, we are seeing some duplication with a very high volume, e.g. single records resent hundreds of times.  That seems like it would require the client to be stuck in some kind of bad state.

One possible utility here would be to attach a Message with data about the current session {e.g. how many times has client tried to send this report, and what the last error was} to each Report Message in HTTP header, so that we could use that in debugging.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/72428db90d5704ce7dcf0df6c078ba168c3708a3

commit 72428db90d5704ce7dcf0df6c078ba168c3708a3
Author: Steven Holte <holte@google.com>
Date: Fri Oct 13 19:47:22 2017

Attach ReportingInfo to UMA+UKM reports.

TBR=torne

Bug: 766244
Change-Id: I27b924f4c4a9b258029fd1853f585277e0b0c448
Reviewed-on: https://chromium-review.googlesource.com/701234
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Richard Coles <torne@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Commit-Queue: Steven Holte <holte@chromium.org>
Cr-Commit-Position: refs/heads/master@{#508785}
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/android_webview/browser/aw_metrics_log_uploader.cc
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/android_webview/browser/aw_metrics_log_uploader.h
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/BUILD.gn
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/metrics_log_uploader.h
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/net/net_metrics_log_uploader.cc
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/net/net_metrics_log_uploader.h
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/net/net_metrics_log_uploader_unittest.cc
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/reporting_service.cc
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/reporting_service.h
[add] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/reporting_service_unittest.cc
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/test_metrics_log_uploader.cc
[modify] https://crrev.com/72428db90d5704ce7dcf0df6c078ba168c3708a3/components/metrics/test_metrics_log_uploader.h