Serve temporary file URL requests in all platforms if enabled.

Serving temporary file URL requests was enabled only for ChromeOS. It's
now expanded to all platforms if in-memory file system is enabled.
Related tests are updated in FileSystemDirUrlRequestJob unittest and
FileSystemURLLoaderFactoryTest browsertest.

Bug: 93417

Change-Id: I600ee8addfe48a00eaff9ff3caa341e1a95ed63e
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1572403
Commit-Queue: Ramin Halavati <rhalavati@chromium.org>
Reviewed-by: Marijn Kruisselbrink <mek@chromium.org>
Cr-Commit-Position: refs/heads/master@{#654350}
6 files changed