Adds flag for enabling/disabling file handling.

This will enable starting implementation on file-handling
behind the flag.

https://chromium-review.googlesource.com/c/chromium/src/+/1589675
is an early prototype of what the implementation might look like.

Bug: 829689
Change-Id: If92cfd86a115ea9cb2985a2cf360b3ba41097089
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1593883
Reviewed-by: Kentaro Hara <haraken@chromium.org>
Reviewed-by: Raymes Khoury <raymes@chromium.org>
Commit-Queue: Jay Harris <harrisjay@chromium.org>
Cr-Commit-Position: refs/heads/master@{#656729}
7 files changed