[Chrome OS] Implement the device wallpaper policy.

chrome/browser/chromeos/login/ui/webui_login_display.cc

Index: chrome/browser/chromeos/login/ui/webui_login_display.cc
diff --git a/chrome/browser/chromeos/login/ui/webui_login_display.cc b/chrome/browser/chromeos/login/ui/webui_login_display.cc
index 5eb3a38e37ddac1284f909758b87cb75655c9295..74ff645d930fca6436b814e36c45aa86f0e75d12 100644
--- a/chrome/browser/chromeos/login/ui/webui_login_display.cc
+++ b/chrome/browser/chromeos/login/ui/webui_login_display.cc
@@ -227,8 +227,11 @@ void WebUILoginDisplay::LoadWallpaper(const AccountId& account_id) {
 }
 
 void WebUILoginDisplay::LoadSigninWallpaper() {
-  WallpaperManager::Get()->SetDefaultWallpaperDelayed(
-      user_manager::SignInAccountId());
+  if (!WallpaperManager::Get()->SetDeviceWallpaperIfApplicable(
+          user_manager::SignInAccountId())) {
+    WallpaperManager::Get()->SetDefaultWallpaperDelayed(
+        user_manager::SignInAccountId());
+  }
 }
 
 void WebUILoginDisplay::OnSigninScreenReady() {