Implement Truncate for SmbFileSystem

Implements Truncate for SmbFileSystem.

Bug: chromium:757625
CQ-DEPEND=CL:879566

Change-Id: Iecf94821ec7237be1fcc07b693c0bdec35903d97
Reviewed-on: https://chromium-review.googlesource.com/889558
Commit-Queue: Allen Vicencio <allenvic@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533164}
2 files changed