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

ash/desktop_background/desktop_background_controller.cc

Index: ash/desktop_background/desktop_background_controller.cc
diff --git a/ash/desktop_background/desktop_background_controller.cc b/ash/desktop_background/desktop_background_controller.cc
new file mode 100644
index 0000000000000000000000000000000000000000..93d8462d836caf92739b4a90126b060e6d41218f
--- /dev/null
+++ b/ash/desktop_background/desktop_background_controller.cc
@@ -0,0 +1,60 @@
+// Copyright (c) 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "ash/desktop_background/desktop_background_controller.h"
+
+#include "ash/desktop_background/desktop_background_resources.h"
+#include "ash/shell.h"
+#include "base/logging.h"
+#include "chrome/browser/chromeos/login/user_manager.h"
+#include "chrome/common/chrome_notification_types.h"
+#include "content/public/browser/notification_service.h"
+#include "grit/ui_resources.h"
+#include "ui/gfx/image/image.h"
+#include "ui/base/resource/resource_bundle.h"
+
+namespace ash {
+
+DesktopBackgroundController::DesktopBackgroundController(){
+  registrar_.Add(
+      this,
+      chrome::NOTIFICATION_DESKTOP_BACKGROUND_CHANGED,
+      content::NotificationService::AllSources());
+  registrar_.Add(
+      this,
+      chrome::NOTIFICATION_LOGIN_USER_CHANGED,
+      content::NotificationService::AllSources());
+}
+
+DesktopBackgroundController::~DesktopBackgroundController() {
+}
+
+void DesktopBackgroundController::OnDesktopBackgroundChange(int index) {
+  DCHECK(index >=0 && index < kDefaultWallpaperCount);
+  Shell::GetInstance()->SetDesktopBackgroundWallpaper(
+      GetDefaultWallpaper(index));
+}
+
+void  DesktopBackgroundController::Observe(int type,
+    const content::NotificationSource& source,
+    const content::NotificationDetails& details) {
+  switch (type) {
+    case chrome::NOTIFICATION_DESKTOP_BACKGROUND_CHANGED: {
+      int index = *content::Details<int>(details).ptr();
+      OnDesktopBackgroundChange(index);
+      break;
+    }
+    case chrome::NOTIFICATION_LOGIN_USER_CHANGED: {
+      chromeos::UserManager* user_manager = chromeos::UserManager::Get();
+      const chromeos::User& user = user_manager->logged_in_user();
+      int index = user_manager->GetUserWallpaper(user.email());
+      OnDesktopBackgroundChange(index);
+      break;
+    }
+    default:
+      NOTREACHED();
+  }
+}
+
+}  // namespace ash