GitLab

Add a method to InstantService to check if a custom background
has been set. Clean up a few places that were checking the
pref directly.

Bug: 873699
Change-Id: I755c6d26cb5fc6cce1239fd796fbfc5e3fb45ce5
Reviewed-on: https://chromium-review.googlesource.com/c/1338091Reviewed-by: Ramya Nagarajan <ramyan@chromium.org>
Commit-Queue: Kyle Milka <kmilka@chromium.org>
Cr-Commit-Position: refs/heads/master@{#610955}