2nd display should show the same background as login/lock screen:

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 1448a21525ef3a0dcef7d8faae23a1c1cf367e79..65a5b601e2d158d763de5f70d9f3dd9fbb5b118b 100644
--- a/ash/desktop_background/desktop_background_view.cc
+++ b/ash/desktop_background/desktop_background_view.cc
@@ -31,8 +31,10 @@ namespace {
 class ShowWallpaperAnimationObserver : public ui::ImplicitAnimationObserver {
  public:
   ShowWallpaperAnimationObserver(aura::RootWindow* root_window,
+                                 int container_id,
                                  views::Widget* desktop_widget)
       : root_window_(root_window),
+        container_id_(container_id),
         desktop_widget_(desktop_widget) {
   }
 
@@ -45,7 +47,7 @@ class ShowWallpaperAnimationObserver : public ui::ImplicitAnimationObserver {
     internal::RootWindowLayoutManager* root_window_layout =
         static_cast<internal::RootWindowLayoutManager*>(
             root_window_->layout_manager());
-    root_window_layout->SetBackgroundWidget(desktop_widget_);
+    root_window_layout->SetBackgroundWidget(desktop_widget_, container_id_);
 
     ash::Shell::GetInstance()->
         user_wallpaper_delegate()->OnWallpaperAnimationFinished();
@@ -54,6 +56,7 @@ class ShowWallpaperAnimationObserver : public ui::ImplicitAnimationObserver {
   }
 
   aura::RootWindow* root_window_;
+  int container_id_;
   views::Widget* desktop_widget_;
 
   DISALLOW_COPY_AND_ASSIGN(ShowWallpaperAnimationObserver);
@@ -138,7 +141,7 @@ void DesktopBackgroundView::ShowContextMenuForView(views::View* source,
   Shell::GetInstance()->ShowBackgroundMenu(GetWidget(), point);
 }
 
-void CreateDesktopBackground(aura::RootWindow* root_window) {
+void CreateDesktopBackground(aura::RootWindow* root_window, int container_id) {
   DesktopBackgroundController* controller = ash::Shell::GetInstance()->
       desktop_background_controller();
   views::Widget* desktop_widget = new views::Widget;
@@ -148,8 +151,7 @@ void CreateDesktopBackground(aura::RootWindow* root_window) {
   params.delegate = view;
   if (controller->GetWallpaper().empty())
     params.transparent = true;
-  params.parent = root_window->GetChildById(
-      ash::internal::kShellWindowId_DesktopBackgroundContainer);
+  params.parent = root_window->GetChildById(container_id);
   desktop_widget->Init(params);
   desktop_widget->SetContentsView(view);
   ash::SetWindowVisibilityAnimationType(
@@ -163,6 +165,7 @@ void CreateDesktopBackground(aura::RootWindow* root_window) {
                                             layer()->GetAnimator());
   settings.SetPreemptionStrategy(ui::LayerAnimator::ENQUEUE_NEW_ANIMATION);
   settings.AddObserver(new ShowWallpaperAnimationObserver(root_window,
+                                                          container_id,
                                                           desktop_widget));
   desktop_widget->Show();
   desktop_widget->GetNativeView()->SetName("DesktopBackgroundView");