Convert TestingProfile TestingFactories to use Callback

Change TestingFactories to use base::Callback instead of
function pointers to allow removal of the deprecated
methods of BCKSF.

Bug: 809610
Change-Id: I10cde9d5c7afefe8f9eeb0e018b47bebdd269604
Reviewed-on: https://chromium-review.googlesource.com/1243130
Commit-Queue: Sylvain Defresne <sdefresne@chromium.org>
Reviewed-by: Julian Pastarmov <pastarmovj@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: David Roger <droger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#594675}