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

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 1220f5e686d7d2774802a452dd6e979e67d6de0c..12432078b7a2a08c7a1ddb82e4aedd792e5e38d2 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -8,6 +8,9 @@
 
 #include "ash/app_list/app_list.h"
 #include "ash/ash_switches.h"
+#include "ash/desktop_background/desktop_background_controller.h"
+#include "ash/desktop_background/desktop_background_resources.h"
+#include "ash/desktop_background/desktop_background_view.h"
 #include "ash/drag_drop/drag_drop_controller.h"
 #include "ash/focus_cycler.h"
 #include "ash/ime/input_method_event_filter.h"
@@ -474,6 +477,7 @@ void Shell::Init() {
   AddRootWindowEventFilter(tooltip_controller_.get());
 
   drag_drop_controller_.reset(new internal::DragDropController);
+  desktop_background_controller_.reset(new DesktopBackgroundController);
   power_button_controller_.reset(new PowerButtonController);
   video_detector_.reset(new VideoDetector);
   window_cycle_controller_.reset(new WindowCycleController);
@@ -539,6 +543,15 @@ void Shell::ToggleAppList() {
   app_list_->SetVisible(!app_list_->IsVisible());
 }
 
+void Shell::SetDesktopBackgroundWallpaper(const SkBitmap& wallpaper) {
+  if (desktop_background_mode_ == BACKGROUND_SOLID_COLOR)
+    return;
+  DCHECK(root_window_layout_->background_widget());
+  static_cast<internal::DesktopBackgroundView*>(
+      root_window_layout_->background_widget()->widget_delegate())->
+      SetWallpaper(wallpaper);
+}
+
 void Shell::SetDesktopBackgroundMode(BackgroundMode mode) {
   if (mode == BACKGROUND_SOLID_COLOR) {
     // Set a solid black background.