A note: The desktop iOS promotion is Windows-only (and it's
guarded everywhere by OS_WIN). Will be hard to do that conversion on another
platform. Ideally someone with a Windows development environment would make this change.

As a further note, I verified that this code is still live code, i.e., removing it from the tree is not an option.

Jochen, do you have the ability to do development on Windows? If so, this would be a great bug to take.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/b1fed93e44779b5c870b94087ef09ad0e5a73bc5

commit b1fed93e44779b5c870b94087ef09ad0e5a73bc5
Author: Jochen Eisinger <jochen@chromium.org>
Date: Mon Jul 09 12:23:16 2018

Move DesktopIOSPromotion to IdentityManager

BUG= 798048 
R=blundell@chromium.org

Change-Id: Icd2d93fd2b9e455383b2c84b6db6ac0f945f8f78
Reviewed-on: https://chromium-review.googlesource.com/1126926
Commit-Queue: Jochen Eisinger <jochen@chromium.org>
Reviewed-by: Colin Blundell <blundell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#573275}
[modify] https://crrev.com/b1fed93e44779b5c870b94087ef09ad0e5a73bc5/chrome/browser/ui/desktop_ios_promotion/desktop_ios_promotion_bubble_controller_unittest.cc
[modify] https://crrev.com/b1fed93e44779b5c870b94087ef09ad0e5a73bc5/chrome/browser/ui/desktop_ios_promotion/desktop_ios_promotion_util_unittest.cc
[modify] https://crrev.com/b1fed93e44779b5c870b94087ef09ad0e5a73bc5/chrome/browser/ui/desktop_ios_promotion/sms_service.cc
[modify] https://crrev.com/b1fed93e44779b5c870b94087ef09ad0e5a73bc5/chrome/browser/ui/desktop_ios_promotion/sms_service.h
[modify] https://crrev.com/b1fed93e44779b5c870b94087ef09ad0e5a73bc5/chrome/browser/ui/desktop_ios_promotion/sms_service_factory.cc
[modify] https://crrev.com/b1fed93e44779b5c870b94087ef09ad0e5a73bc5/chrome/browser/ui/desktop_ios_promotion/sms_service_unittest.cc