Move all wallpaper file loading and decoding from DesktopBackgroundController to WallpaperManager.

ash/shell/content_client/shell_browser_main_parts.cc

Index: ash/shell/content_client/shell_browser_main_parts.cc
diff --git a/ash/shell/content_client/shell_browser_main_parts.cc b/ash/shell/content_client/shell_browser_main_parts.cc
index 7a745c6b833e3f92e756f3d833736edaacf4bde7..02017e62d673f71e97f191ce7ea75e31104e6b73 100644
--- a/ash/shell/content_client/shell_browser_main_parts.cc
+++ b/ash/shell/content_client/shell_browser_main_parts.cc
@@ -37,6 +37,7 @@
 #endif
 
 #if defined(OS_CHROMEOS)
+#include "chrome/browser/chromeos/login/wallpaper_manager.h"
 #include "chromeos/audio/cras_audio_handler.h"
 #include "chromeos/dbus/dbus_thread_manager.h"
 #endif
@@ -134,8 +135,10 @@ void ShellBrowserMainParts::PreMainMessageLoopRun() {
 
   ash::shell::InitWindowTypeLauncher();
 
-  Shell::GetInstance()->desktop_background_controller()->SetDefaultWallpaper(
-      false /* is_guest */);
+#if defined(OS_CHROMEOS)
+  chromeos::WallpaperManager::Get()->
+      SetDefaultWallpaperDelayed(chromeos::UserManager::kSignInUser);
+#endif
 
   ash::Shell::GetPrimaryRootWindow()->GetHost()->Show();
 }