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

ash/desktop_background/desktop_background_view.cc

 // 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.
 
 #include "ash/desktop_background/desktop_background_view.h"
 
 #include <limits>
 
 #include "ash/ash_export.h"
 #include "ash/desktop_background/desktop_background_controller.h"
 #include "ash/shell.h"
 #include "ash/shell_window_ids.h"
-#include "ash/wm/root_window_layout_manager.h"
 #include "ash/wm/window_animations.h"
 #include "base/message_loop.h"
 #include "base/utf_string_conversions.h"
 #include "grit/ui_resources.h"
 #include "ui/aura/root_window.h"
 #include "ui/base/resource/resource_bundle.h"
 #include "ui/compositor/layer.h"
 #include "ui/compositor/layer_animation_observer.h"
 #include "ui/compositor/scoped_layer_animation_settings.h"
 #include "ui/gfx/canvas.h"
 #include "ui/gfx/image/image.h"
 #include "ui/views/widget/widget.h"
 
 namespace ash {
 namespace internal {
 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) {
   }
 
   virtual ~ShowWallpaperAnimationObserver() {
   }
 
  private:
   // Overridden from ui::ImplicitAnimationObserver:
   virtual void OnImplicitAnimationsCompleted() OVERRIDE {
-    internal::RootWindowLayoutManager* root_window_layout =
-        static_cast<internal::RootWindowLayoutManager*>(
-            root_window_->layout_manager());
-    root_window_layout->SetBackgroundWidget(desktop_widget_);
-
     ash::Shell::GetInstance()->
         user_wallpaper_delegate()->OnWallpaperAnimationFinished();
 
     MessageLoop::current()->DeleteSoon(FROM_HERE, this);
   }
 
   aura::RootWindow* root_window_;
+  int container_id_;
   views::Widget* desktop_widget_;
 
   DISALLOW_COPY_AND_ASSIGN(ShowWallpaperAnimationObserver);
 };
 
 }  // namespace
 
 // For our scaling ratios we need to round positive numbers.
 static int RoundPositive(double x) {
   return static_cast<int>(floor(x + 0.5));
@@ skipping 64 matching lines @@
 
 bool DesktopBackgroundView::OnMousePressed(const views::MouseEvent& event) {
   return true;
 }
 
 void DesktopBackgroundView::ShowContextMenuForView(views::View* source,
                                                    const gfx::Point& point) {
   Shell::GetInstance()->ShowBackgroundMenu(GetWidget(), point);
 }
 
-void CreateDesktopBackground(aura::RootWindow* root_window) {
+views::Widget* CreateDesktopBackground(aura::RootWindow* root_window,
+                                       int container_id) {
   DesktopBackgroundController* controller = ash::Shell::GetInstance()->
       desktop_background_controller();
   views::Widget* desktop_widget = new views::Widget;
   views::Widget::InitParams params(
       views::Widget::InitParams::TYPE_WINDOW_FRAMELESS);
   DesktopBackgroundView* view = new DesktopBackgroundView();
   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::WindowVisibilityAnimationType animation_type =
       ash::Shell::GetInstance()->user_wallpaper_delegate()->GetAnimationType();
   ash::SetWindowVisibilityAnimationType(desktop_widget->GetNativeView(),
                                         animation_type);
   ash::SetWindowVisibilityAnimationTransition(desktop_widget->GetNativeView(),
                                               ash::ANIMATE_SHOW);
   desktop_widget->SetBounds(params.parent->bounds());
   ui::ScopedLayerAnimationSettings settings(
       desktop_widget->GetNativeView()->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");
+  return desktop_widget;
 }
 
 }  // namespace internal
 }  // namespace ash