Make the lifetime of wallpaper manager more clear.

chrome/browser/chromeos/chrome_browser_main_chromeos.cc

Index: chrome/browser/chromeos/chrome_browser_main_chromeos.cc
diff --git a/chrome/browser/chromeos/chrome_browser_main_chromeos.cc b/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
index 0556a2eeb97b98fb11fad8229069f67243d8d451..9bdf63f0bdbea9529412cb8e6bbb09045ee8eb1c 100644
--- a/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
+++ b/chrome/browser/chromeos/chrome_browser_main_chromeos.cc
@@ -423,6 +423,7 @@ void ChromeBrowserMainPartsChromeos::PreProfileInit() {
 
   // Add observers for WallpaperManager. This depends on PowerManagerClient,
   // TimezoneSettings and CrosSettings.
+  WallpaperManager::Initialize();
   WallpaperManager::Get()->AddObservers();
 
   base::PostTaskAndReplyWithResult(
@@ -727,7 +728,7 @@ void ChromeBrowserMainPartsChromeos::PostMainMessageLoopRun() {
   // that the UserManager has no URLRequest pending (see
   // http://crbug.com/276659).
   g_browser_process->platform_part()->user_manager()->Shutdown();
-  WallpaperManager::Get()->Shutdown();
+  WallpaperManager::Shutdown();
 
   // Let the DeviceDisablingManager unregister itself as an observer of the
   // CrosSettings singleton before it is destroyed.