Code was removed:

commit 476061989ab2a70acf80895c206fe8b41dbdf15a
Author: Marc Treib <treib@chromium.org>
Date:   Thu Feb 8 17:20:38 2018 +0000

    Cleanup: Remove Sync Attachments code
    
    Sync Attachments were never launched, and there are no plans to.
    This CL removes all the code, but doesn't update any protos yet.
    
    TBRing a bunch of mechanical, test-only changes.
    TBR=jochen
    
    Bug:  758319 
    Change-Id: I3cff4d74293eead97deceedb1567b94ca799d05f
    Reviewed-on: https://chromium-review.googlesource.com/899004
    Commit-Queue: Marc Treib <treib@chromium.org>
    Reviewed-by: Ramin Halavati <rhalavati@chromium.org>
    Reviewed-by: Nicolas Zea <zea@chromium.org>
    Cr-Commit-Position: refs/heads/master@{#535417}