Enable user change background image in settings page in Aura build.

chrome/browser/chromeos/chrome_browser_main_chromeos.h

Index: chrome/browser/chromeos/chrome_browser_main_chromeos.h
diff --git a/chrome/browser/chromeos/chrome_browser_main_chromeos.h b/chrome/browser/chromeos/chrome_browser_main_chromeos.h
index 156dc58b20070bcbaa2331f19d60d242e948a1b1..5bfc42959a4691ab6b499ce6a6f35e175391ad52 100644
--- a/chrome/browser/chromeos/chrome_browser_main_chromeos.h
+++ b/chrome/browser/chromeos/chrome_browser_main_chromeos.h
@@ -14,6 +14,10 @@ class ResumeObserver;
 class ScreenLockObserver;
 class SessionManagerObserver;
 
+#if defined(USE_ASH)
+class DesktopBackgroundObserver;
+#endif
+
 #if defined(USE_AURA)
 class InitialBrowserWindowObserver;
 class PowerButtonObserver;
@@ -47,6 +51,10 @@ class ChromeBrowserMainPartsChromeos : public ChromeBrowserMainPartsLinux {
   scoped_ptr<chromeos::ScreenLockObserver> screen_lock_observer_;
   scoped_ptr<chromeos::SessionManagerObserver> session_manager_observer_;
 
+#if defined(USE_ASH)
+  scoped_ptr<chromeos::DesktopBackgroundObserver> desktop_background_observer_;
+#endif
+
 #if defined(USE_AURA)
   scoped_ptr<chromeos::InitialBrowserWindowObserver>
       initial_browser_window_observer_;