GitLab

1) Emphasize the default wallpaper selection order in
   DoSetDefaultWallpaper (renamed to SetDefaultWallpaperImpl).
   Create two additional member variables to store the customized
   default wallpaper file paths to make the distinction with a regular
   default wallpaper (ie. from the command line). Previously, these
   two are mixed in the code.

2) Rename |SetDefaultWallpaperPath| to
   |SetCustomizedDefaultWallpaperImpl|.

3) |SetDefaultWallpaperPathsFromCommandLine| is removed. We don't have
   the need to cache the values which come from the command line.

TBR=oshima@chromium.org, ochang@chromium.org

Test: Manual (device/Linux build), ash_unittests, browser tests
Bug: 792233
Change-Id: I09876e23ea7609c7b7e876d4daf79c4fa35088c5
Reviewed-on: https://chromium-review.googlesource.com/808092Reviewed-by: Wenzhao (Colin) Zang <wzang@chromium.org>
Reviewed-by: Alexander Alekseev <alemate@chromium.org>
Reviewed-by: Oliver Chang <ochang@chromium.org>
Reviewed-by: Mitsuru Oshima <oshima@chromium.org>
Reviewed-by: Xiaoqian Dai <xdai@chromium.org>
Commit-Queue: Wenzhao (Colin) Zang <wzang@chromium.org>
Cr-Commit-Position: refs/heads/master@{#523324}