mash: Migrate wallpaper controllers to ash/common.

ash/default_wallpaper_delegate.cc

Index: ash/default_wallpaper_delegate.cc
diff --git a/ash/default_wallpaper_delegate.cc b/ash/default_wallpaper_delegate.cc
index 6139a4d2e3aac4ee3887a50d5312e0c6611dec99..8de44717983aeae2ccb47c5c983340a1a1d14dde 100644
--- a/ash/default_wallpaper_delegate.cc
+++ b/ash/default_wallpaper_delegate.cc
@@ -4,8 +4,8 @@
 
 #include "ash/default_wallpaper_delegate.h"
 
-#include "ash/shell.h"
-#include "ash/wallpaper/wallpaper_controller.h"
+#include "ash/common/wallpaper/wallpaper_controller.h"
+#include "ash/common/wm_shell.h"
 #include "ui/wm/core/window_animations.h"
 
 namespace ash {
@@ -28,7 +28,7 @@ bool DefaultWallpaperDelegate::ShouldShowInitialAnimation() {
 void DefaultWallpaperDelegate::UpdateWallpaper(bool clear_cache) {}
 
 void DefaultWallpaperDelegate::InitializeWallpaper() {
-  ash::Shell::GetInstance()->wallpaper_controller()->CreateEmptyWallpaper();
+  WmShell::Get()->wallpaper_controller()->CreateEmptyWallpaper();
 }
 
 void DefaultWallpaperDelegate::OpenSetWallpaperPage() {}