[NTP] Add Google Photos option for custom backgrounds

Allow users to select one of their photos from Google Photos and set it
as the NTP background image. Currently only supports users who are
already signed in to their Google account.

Bug: 848012
Cq-Include-Trybots: luci.chromium.try:closure_compilation
Change-Id: Idef07f3cd107199a8e308fc883c96b9a8da37b1e
Reviewed-on: https://chromium-review.googlesource.com/1130100
Commit-Queue: Kyle Milka <kmilka@chromium.org>
Reviewed-by: Mathieu Perreault <mathp@chromium.org>
Cr-Commit-Position: refs/heads/master@{#574666}
8 files changed