cros: Remove references to ash::MultiProfileUMA from chrome/browser

For out-of-process ash code in //chrome cannot call directly into
//ash. See //ash/README.md

* Deprecate MultiProfile.SessionMode since there is only one mode now
* Deprecate MultiProfile.TeleportWindow since it was not being
  maintained
* Migrate metrics only recorded by chrome into //chrome/browser
* Clean up some comments about MultiWindowUserManager

windows between accounts, verify MultiProfile.* counts in

Bug: 766407
Test: unit_tests, manually sign in multiple users and teleport
chrome: //histograms
Change-Id: I3a5f21be9504268d91c66090512c42ac293b18ad
Reviewed-on: https://chromium-review.googlesource.com/1036200


Commit-Queue: James Cook <jamescook@chromium.org>
Reviewed-by: Evan Stade <estade@chromium.org>
Reviewed-by: Ilya Sherman <isherman@chromium.org>
Cr-Commit-Position: refs/heads/master@{#555085}