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..d9e2ff556e30f2c088cd20d160784082eb543fc5 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"
@@ -202,9 +203,11 @@ 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);
-  else
-    shell->SetDesktopBackgroundMode(ash::Shell::BACKGROUND_IMAGE);
+    shell->SetDesktopBackgroundSolidColorMode();
+  else {
+    shell->SetDesktopBackgroundImageMode(shell->
+        desktop_background_controller()->GetPreviouseWallpaper());
+  }
   return true;
 }