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

ash/desktop_background/desktop_background_resources.h

Index: ash/desktop_background/desktop_background_resources.h
diff --git a/ash/desktop_background/desktop_background_resources.h b/ash/desktop_background/desktop_background_resources.h
new file mode 100644
index 0000000000000000000000000000000000000000..1bcfdf88e1a2476d86c62a11a89483054cd822bd
--- /dev/null
+++ b/ash/desktop_background/desktop_background_resources.h
@@ -0,0 +1,19 @@
+// 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_RESOURCES_H_
+#define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_RESOURCES_H_
+
+class SkBitmap;
+
+namespace ash {
+
+int GetDefaultWallpaperIndex();
+int GetWallpaperCount();
+const SkBitmap& GetWallpaper(int index);
+const SkBitmap& GetWallpaperThumbnail(int index);
+
+}  // namespace ash
+
+#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_RESOURCES_H_