[Mac] Move the "Customize Touch Bar" Menu Item

Move the "Customize Touch Bar" menu item so that it's the third item in the
Views menu.

This is done by removing "setAutomaticCustomizeTouchBarMenuItemEnabled"
and manually adding the item in MainMenu.xib. AppKit will name and validate
the menu item, and hides it on systems that do not have a Touch Bar. However,
this is only available in 10.12.1+. We manually have to remove that item if
it's not supported.

See "The Customization Menu Item" section in the following link for more
details: https://developer.apple.com/reference/appkit/nstouchbar

BUG=716185

Review-Url: https://codereview.chromium.org/2865763002
Cr-Commit-Position: refs/heads/master@{#470641}
5 files changed