UpdateMaxNumberKey calls are moved to clients, who do have the
dictionary-holder.  ::Add should basically always UpdateMaxNumberKey. I'm
reducing the number of entry points before looking into how to guarantee this.

Bug: 
Change-Id: Iefe8a7fdf7c1e0a6d731bfd948d22849714498a9
Reviewed-on: https://chromium-review.googlesource.com/542895
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46104}