GitLab

Three changes:
 - Add the icons for desktop context menu options.
 - Make the "Autohide Shelf" option a regular menu option.
   - This is because touchable menu items do not use the "check" type
     and was OKed by UX.
 - Remove the "Autohide" and "Shelf position" items in tablet mode.
   - This is requested by UX.

Bug: 850134
Change-Id: I4bc7912687fbd8f1c3543301be511ac02277a859
Reviewed-on: https://chromium-review.googlesource.com/1159735
Commit-Queue: Alex Newcomer <newcomer@chromium.org>
Reviewed-by: Xiyuan Xia <xiyuan@chromium.org>
Cr-Commit-Position: refs/heads/master@{#580379}