GitLab

Don't delete feedback reports files on disk on the
report destruction. This leads to losing pending reports
on sign out or reboot. Instead explicitly delete the files
once successfully uploaded, or when a no-retry failure occurs.

BUG=851687
TEST=Added new test.

Change-Id: I64caf16f63ea73c1888d8b097543e9eacabc1d9e
Reviewed-on: https://chromium-review.googlesource.com/1099758
Commit-Queue: Ahmed Fakhry <afakhry@chromium.org>
Reviewed-by: Rahul Chaturvedi <rkc@chromium.org>
Cr-Commit-Position: refs/heads/master@{#567111}