New approach is to do this in ReportingService. OnURLFetchComplete should pass a boolean to OnUploadComplete specifying whether the current attempt was over HTTP or HTTPS, if the latter, ReportingService should schedule a retry over HTTP for the next attempt.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/75b352f3637ba5e1c7e37c054f3b1c29d15dcfdc

commit 75b352f3637ba5e1c7e37c054f3b1c29d15dcfdc
Author: Carlos IL <carlosil@chromium.org>
Date: Tue Nov 07 01:43:02 2017

UMA now retries over HTTP on upload failures.

The UMA client now retries uploads over an HTTP connection if HTTPS
fails. Logs uploaded over HTTP are encrypted first, along with their 
hash and ReportingInfo headers using the encrypted messages component.
Currently this only happens if chrome is started with the
--retry-uma-over-http flag. Tests were also added that validate HTTP
uploads are encrypted and HTTPS ones are not.
In a future CL the UMA.LogUpload.ResponseOrErrorCode histogram will be
split so requests made over HTTP have a separate histogram from those
done over HTTPS.

Bug:  769145 
Cq-Include-Trybots: master.tryserver.chromium.mac:ios-simulator-cronet
Change-Id: Id0671c49f6bd979343d7e88e04938f567005375e
Reviewed-on: https://chromium-review.googlesource.com/727264
Reviewed-by: Steven Holte <holte@chromium.org>
Reviewed-by: Adrienne Porter Felt <felt@chromium.org>
Reviewed-by: Bo <boliu@chromium.org>
Reviewed-by: Olivier Robin <olivierrobin@chromium.org>
Commit-Queue: Carlos IL <carlosil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#514342}
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