Add Premount to SmbService

- Adds Premount method in SmbService in anticipation of
  SmbProviderClient::Premount's implementation.
- Adds reponse callback method to connect MountOptions of the
  preconfigured share to the FileSystem.

Bug: chromium:878502
Test: compiles
Change-Id: I0c9af981d0cd1f2fd57c5a5ecfec4feef6c127de
Reviewed-on: https://chromium-review.googlesource.com/c/1407660
Commit-Queue: jimmy gong <jimmyxgong@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Bailey Berro <baileyberro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#625488}
2 files changed