The wiring is already done- just need to set the icon here https://cs.chromium.org/chromium/src/chrome/browser/chromeos/smb_client/smb_provider.cc?rcl=e2f2e6458eb9c816f07b12a632ef81e8d3bb44a0&l=28

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/8d1bf34d24837930ef8c58f305c38f6123426dc0

commit 8d1bf34d24837930ef8c58f305c38f6123426dc0
Author: Adolfo Victoria <adokar@google.com>
Date: Fri Jun 08 17:51:10 2018

Add Icons for SMB Provider.

Added the icons for the native SMB client to the theme, this changes
the icon under the "Add New Services" menu in the Files app to the
correct one. Updated the URLs in smb_provider.cc accordingly.

BUG= chromium:842753 
TEST=verified on test device (cave board)

Change-Id: Id4f835f0ea167707c34f35b9022c6f685ce2f958
Reviewed-on: https://chromium-review.googlesource.com/1077548
Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Commit-Queue: Adolfo Higueros <adokar@google.com>
Cr-Commit-Position: refs/heads/master@{#565679}
[add] https://crrev.com/8d1bf34d24837930ef8c58f305c38f6123426dc0/chrome/app/theme/default_100_percent/cros/smb_icon.png
[add] https://crrev.com/8d1bf34d24837930ef8c58f305c38f6123426dc0/chrome/app/theme/default_200_percent/cros/smb_icon.png
[modify] https://crrev.com/8d1bf34d24837930ef8c58f305c38f6123426dc0/chrome/app/theme/theme_resources.grd
[modify] https://crrev.com/8d1bf34d24837930ef8c58f305c38f6123426dc0/chrome/browser/chromeos/smb_client/smb_provider.cc