* Add FileBackend::addShellboxInputFile(), allowing Shellbox to read
directly from a FileBackend. Add generic, FS and Swift
implementations.
* Add FileRepo wrapper, which takes a FileRepo virtual URL.
* Add File::addToShellboxCommand(), which allows a File to be used as
input in a Shellbox command.
* Add configuration.
* Extend FileBackend::getFileHttpUrl(), adding method and ipRange
parameters. Unindent existing code.
I was going to add support for PUT requests, but I reverted it due to
the impossibility of supporting FileBackendMultiWrite. I left the method
parameter in getFileHttpUrl().
Bug: T292322
Change-Id: If9487a0c9586065bf044b69ac04cc7a06b6e8856
(cherry picked from commit 8cdde9dcb03e33332e49aed06aa71b60ae2c9b33)
0be1887f2d