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

ash/desktop_background/desktop_background_view.cc

Index: ash/desktop_background/desktop_background_view.cc
diff --git a/ash/desktop_background/desktop_background_view.cc b/ash/desktop_background/desktop_background_view.cc
index dbf256f0499df461eccbaff9cee46a3b78ca9305..121edb6fdb883616bc61b5215ef1a6e9137a8844 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -29,14 +29,17 @@ static int RoundPositive(double x) {
 // DesktopBackgroundView, public:
 
 DesktopBackgroundView::DesktopBackgroundView() {
-  wallpaper_ = *ui::ResourceBundle::GetSharedInstance().GetImageNamed(
-      IDR_AURA_WALLPAPER_1).ToSkBitmap();
-  wallpaper_.buildMipMap(false);
 }
 
 DesktopBackgroundView::~DesktopBackgroundView() {
 }
 
+void DesktopBackgroundView::SetWallpaper(const SkBitmap& wallpaper) {
+  wallpaper_ = wallpaper;
+  wallpaper_.buildMipMap(false);
+  SchedulePaint();
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 // DesktopBackgroundView, views::View overrides:
 
@@ -92,7 +95,7 @@ views::Widget* CreateDesktopBackground() {
   views::Widget* desktop_widget = new views::Widget;
   views::Widget::InitParams params(
       views::Widget::InitParams::TYPE_WINDOW_FRAMELESS);
-  DesktopBackgroundView* view = new DesktopBackgroundView;
+  DesktopBackgroundView* view = new DesktopBackgroundView();
   params.delegate = view;
   params.parent =
       Shell::GetInstance()->GetContainer(