[BackgroundSync] BGSync missing its initial connection type request

After the switch to NetworkConnectionTracker, the GetConnectionType
call wasn't checking for a synchronous return. In the case of a
synchronous return OnConnectionChanged needs to be called. This led to
BackgroundSyncManager not getting the correct connection type on
startup.

Bug: 900943
Change-Id: I21ffcacdea9cca4c0780f40561e55b10fb9866b1
Reviewed-on: https://chromium-review.googlesource.com/c/1312676
Commit-Queue: Josh Karlin <jkarlin@chromium.org>
Reviewed-by: Peter Beverloo <peter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#604689}