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This change creates the SmbTaskQueue class for queueing FileSystem
operations that will be sent over D-Bus to the Smb Daemon.

BUG=chromium:757625

Change-Id: Id48b8b4abbc5841f42ae1b52dca2e142f2ba6706
Reviewed-on: https://chromium-review.googlesource.com/953134
Commit-Queue: Bailey Berro <baileyberro@chromium.org>
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Cr-Commit-Position: refs/heads/master@{#542899}