Allow download to create a content URI file during intermediate file rename stage

This allows download to create a content URI file during intermediate file
renaming stage.
This file will copy all contents from the temporary file.
Embedders will provide the implementation.

Bug: 931021
Change-Id: I083b33666ba4b4130718c71b5459d056124216ea
Reviewed-on: https://chromium-review.googlesource.com/c/1468822
Reviewed-by: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Min Qin <qinmin@chromium.org>
Reviewed-by: David Trainor <dtrainor@chromium.org>
Commit-Queue: Min Qin <qinmin@chromium.org>
Cr-Commit-Position: refs/heads/master@{#633321}
19 files changed