Add WriteFile to SmbProviderClient

Adds WriteFile to SmbProviderClient and FakeSmbProviderClient.

Bug: chromium:757625
Change-Id: I00f09ad71787dc4db922b318e0ae7afbf845ea46
Reviewed-on: https://chromium-review.googlesource.com/889559
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Allen Vicencio <allenvic@chromium.org>
Cr-Commit-Position: refs/heads/master@{#533779}
4 files changed