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

ash/desktop_background/desktop_background_controller.h

Index: ash/desktop_background/desktop_background_controller.h
diff --git a/ash/desktop_background/desktop_background_controller.h b/ash/desktop_background/desktop_background_controller.h
index b575654bdd60a65231d974e51d94eb54d41cd78e..b9278055c3e47ac19a3a9253f82df37d2792605b 100644
--- a/ash/desktop_background/desktop_background_controller.h
+++ b/ash/desktop_background/desktop_background_controller.h
@@ -13,6 +13,7 @@
 #include "base/memory/weak_ptr.h"
 #include "third_party/skia/include/core/SkBitmap.h"
 #include "third_party/skia/include/core/SkColor.h"
+#include "ui/compositor/layer.h"
 #include "ui/gfx/image/image_skia.h"
 
 namespace aura {
@@ -94,25 +95,38 @@ class ASH_EXPORT DesktopBackgroundController {
   // is SystemGestureEventFilterTest.ThreeFingerSwipe.
   void CreateEmptyWallpaper();
 
+  // Create desktop views on Lock Screen layer.
+  void CreateLockScreenDesktops();
+
+  // Remove all desktop views on Lock Screen layer created by
+  // CreateLockScreenDesktops.
+  void RemoveLockScreenDesktops();
+
  private:
   // An operation to asynchronously loads wallpaper.
   class WallpaperOperation;
 
   struct WallpaperData;
 
-  // Creates a new background widget using the current wallpapaer image and
-  // use it as a background of the |root_window|. Deletes the old widget if any.
-  void SetDesktopBackgroundImage(aura::RootWindow* root_window);
-
-  // Update the background of all root windows using the current wallpaper image
-  // in |current_wallpaper_|.
-  void UpdateDesktopBackgroundImageMode();
+  // Creates and adds component for current mode (either Widget or Layer) to
+  // |root_window|.
+  void InstallComponent(aura::RootWindow* root_window);
 
+  // Creates view for all root windows, or notifies them to repaint if they
+  // already exist.
+  void SetDesktopBackgroundImageMode();
   // Creates a new background widget and sets the background mode to image mode.
   // Called after wallpaper loaded successfully.
   void OnWallpaperLoadCompleted(scoped_refptr<WallpaperOperation> wo);
 
+  // Add layer with solid |color| to container |container_id| in |root_window|
+  ui::Layer* SetColorLayerForContainer(SkColor color,
+                                 aura::RootWindow* root_window,
+                                 int container_id);
+
   // Can change at runtime.
+  bool locked_;
+
   BackgroundMode desktop_background_mode_;
 
   SkColor background_color_;