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If a download is interrupted in a terminal state, the information
will be written to both history DB and in-progress DB. And the in-progress
DB info will later be erased when download history is loaded. However,
if Chrome crashes during the write, history DB could contain more recent
information. If the same download is resumed in reduced mode later, loading
the history DB could delete that download, causing Chrome to delete the
DownloadFile object on UI thread while it is reading data on download
task runner.
This CL fixes the issue by:
1. Force in-progress DB to write download information immediately if
a download is in a terminal state.
2. If a download is in terminal state in history DB and an in-progress
DB version is already in-progress, ignore the history DB version and
request it to be deleted. This matches the existing behavior if only
history DB is used. (If only history DB is used, a crash before download
terminal state is written to disk will make the download to be able to
resume, even if a failed notification is already shown).

BUG=1009839

Change-Id: Ic8621754e4961f665f3d42452a4e3794cbbc82bf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1898647
Commit-Queue: Min Qin <qinmin@chromium.org>
Reviewed-by: Xing Liu <xingliu@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#713998}