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

ash/desktop_background/desktop_background_controller.h

Index: ash/desktop_background/desktop_background_controller.h
diff --git a/ash/desktop_background/desktop_background_controller.h b/ash/desktop_background/desktop_background_controller.h
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+// 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.
+
+#ifndef ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
+#define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_
+#pragma once
+
+#include "ash/ash_export.h"
+#include "base/basictypes.h"
+
+class SkBitmap;
+
+namespace ash {
+
+// A class to listen for login and desktop background change events and set the
+// corresponding default wallpaper in Aura shell.
+class ASH_EXPORT DesktopBackgroundController {
+ public:
+  enum BackgroundMode {
+    BACKGROUND_IMAGE,
+    BACKGROUND_SOLID_COLOR
+  };
+
+  DesktopBackgroundController();
+  virtual ~DesktopBackgroundController();
+
+  // Get the desktop background mode.
+  BackgroundMode desktop_background_mode() const {
+    return desktop_background_mode_;
+  }
+
+  // Change the desktop background image to wallpaper with |index|.
+  void OnDesktopBackgroundChanged(int index);
+
+  // Sets the desktop background to image mode and create a new background
+  // widget with |wallpaper|.
+  void SetDesktopBackgroundImageMode(const SkBitmap& wallpaper);
+
+  // Sets the desktop background to image mode and create a new background
+  // widget with default wallpaper.
+  void SetDefaultDesktopBackgroundImage();
+
+  // Sets the desktop background to image mode and create a new background
+  // widget with previous selected wallpaper at run time.
+  void SetPreviousDesktopBackgroundImage();
+
+  // Sets the desktop background to solid color mode and create a solid color
+  // layout.
+  void SetDesktopBackgroundSolidColorMode();
+
+ private:
+  // We need to cache the previously used wallpaper index. So when users switch
+  // desktop background color mode at run time, we can directly switch back to
+  // the user selected wallpaper in image mode.
+  int previous_wallpaper_index_;
+
+  // Can change at runtime.
+  BackgroundMode desktop_background_mode_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundController);
+};
+
+}  // namespace ash
+
+#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_CONTROLLER_H_