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

ash/accelerators/accelerator_controller.cc

Index: ash/accelerators/accelerator_controller.cc
diff --git a/ash/accelerators/accelerator_controller.cc b/ash/accelerators/accelerator_controller.cc
index 5e6a14276291033ea724153515d32c5a9e0a30e7..8c03f8bfea1a530aecfae97a744871e85a36f326 100644
--- a/ash/accelerators/accelerator_controller.cc
+++ b/ash/accelerators/accelerator_controller.cc
@@ -4,6 +4,7 @@
 
 #include "ash/accelerators/accelerator_controller.h"
 
+#include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/caps_lock_delegate.h"
 #include "ash/ime_control_delegate.h"
 #include "ash/launcher/launcher.h"
@@ -200,11 +201,13 @@ bool HandleRotateScreen() {
 }
 
 bool HandleToggleDesktopBackgroundMode() {
-  ash::Shell* shell = ash::Shell::GetInstance();
-  if (shell->desktop_background_mode() == ash::Shell::BACKGROUND_IMAGE)
-    shell->SetDesktopBackgroundMode(ash::Shell::BACKGROUND_SOLID_COLOR);
+  ash::DesktopBackgroundController* desktop_background_controller =
+      ash::Shell::GetInstance()->desktop_background_controller();
+  if (desktop_background_controller->desktop_background_mode() ==
+      ash::DesktopBackgroundController::BACKGROUND_IMAGE)
+    desktop_background_controller->SetDesktopBackgroundSolidColorMode();
   else
-    shell->SetDesktopBackgroundMode(ash::Shell::BACKGROUND_IMAGE);
+    desktop_background_controller->SetPreviousDesktopBackgroundImage();
   return true;
 }