GitLab

ArcWallpaperService now observes wallpaper change
and notifies Android, which will use it to broadcast
ACTION_WALLPAPER_CHANGED.

Test=Change wallpaper with CrOS wallpaper picker
  and verify with Android app that listens wallpaper
  changed broadcast.

Bug=642465

Review-Url: https://codereview.chromium.org/2345153002
Cr-Commit-Position: refs/heads/master@{#419303}