ash: Use local state directly

- Pass local state PrefService to ash directly during init instead
  of getting it through prefs::ConnectToPrefService.
- Simplify DisplayPrefs since local state is passed directly to ash;
- Update WallpaperController to handle local state is available
  before its Init call and remove obsolete IgnoreShowUserWallpaper;

Bug: 958237
Change-Id: I981fa3cbd5a2a6ebd2a088c678608b601a1fde2f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1606567
Commit-Queue: Xiyuan Xia <xiyuan@chromium.org>
Reviewed-by: Scott Violet <sky@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Reviewed-by: Ahmed Fakhry <afakhry@chromium.org>
Cr-Commit-Position: refs/heads/master@{#659631}
17 files changed