Revert of Remove SVN and File support from gclient (patchset #4 id:60001 of https://codereview.chromium.org/2398493004/ )

Reason for revert:
The Chrome buildbots pass "--transitive" still. Removing the option causes them to fail to build.

Example:

https://uberchromegw.corp.google.com/i/chromeos.chrome/builders/x86-alex-tot-chrome-pfq-informational/builds/21555

Original issue's description:
> Remove SVN and File support from gclient
>
> FileImpl was only usable with SVN.
>
> R=maruel@chromium.org
> BUG=641588
>
> Committed: https://chromium.googlesource.com/chromium/tools/depot_tools/+/b3a24c3fd5159972f58063967a9c07ef724ff97b

TBR=maruel@chromium.org,agable@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=641588

Review-Url: https://codereview.chromium.org/2405173003