DisplaySettings: Lazily load wallpapers

Load the wallpaper in a background action instead of on the main thread.

This reduces the time to first paint, and makes the UI feel more
responsive when clicking on wallpaper thumbnails.

The behavior of the method is changed slightly to return true if it
succesfully "loads" the empty path. This makes the API a little more
consistent, where "true" means "I made changes" and "false" means "I did
not make changes". No call sites currently use the return value, so no
changes are needed to those.

0 files changed, 0 insertions, 0 deletions