The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/cac62e3f938a539c6f8212816e156dc516866310

commit cac62e3f938a539c6f8212816e156dc516866310
Author: Wenzhao Zang <wzang@chromium.org>
Date: Tue Dec 12 04:05:28 2017

wallpaper refactoring: Move SetDefaultWallpaper to WallpaperController

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/808092
Reviewed-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}
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/ash/public/interfaces/wallpaper.mojom
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/ash/wallpaper/wallpaper_controller.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/ash/wallpaper/wallpaper_controller.h
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/ash/wallpaper/wallpaper_controller_unittest.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/arc/wallpaper/arc_wallpaper_service_unittest.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/customization/customization_wallpaper_downloader_browsertest.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/extensions/wallpaper_api.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/extensions/wallpaper_private_api.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager.h
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager_browsertest.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager_test_utils.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/chromeos/login/users/wallpaper/wallpaper_manager_test_utils.h
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/ui/ash/test_wallpaper_controller.cc
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/ui/ash/test_wallpaper_controller.h
[modify] https://crrev.com/cac62e3f938a539c6f8212816e156dc516866310/chrome/browser/ui/ash/wallpaper_controller_client.cc