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

ash/desktop_background/desktop_background_widget_controller.h

Index: ash/desktop_background/desktop_background_widget_controller.h
diff --git a/ash/desktop_background/desktop_background_widget_controller.h b/ash/desktop_background/desktop_background_widget_controller.h
new file mode 100644
index 0000000000000000000000000000000000000000..fe07ef30430b656ed0ad7f90537e09f5de62b491
--- /dev/null
+++ b/ash/desktop_background/desktop_background_widget_controller.h
@@ -0,0 +1,54 @@
+// 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.
+
+#ifndef ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_WIDGET_CONTROLLER_H_
+#define ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_WIDGET_CONTROLLER_H_
+
+#include "base/memory/scoped_ptr.h"
+#include "ui/aura/window_property.h"
+#include "ui/compositor/layer.h"
+#include "ui/views/widget/widget.h"
+
+namespace ash {
+namespace internal {
+
+// This class hides difference between two possible background implementations:
+// effective Layer-based for solid color, and Widget-based for images.
+class DesktopBackgroundWidgetController {
+ public:
+  // Create
+  explicit DesktopBackgroundWidgetController(views::Widget* widget);
+  explicit DesktopBackgroundWidgetController(ui::Layer* layer);
+
+  ~DesktopBackgroundWidgetController();
+
+  // Set bounds of component that draws background.
+  void SetBounds(gfx::Rect bounds);
+
+  // Move component from |src_container| in |root_window| to |dest_container|.
+  // It is required for lock screen, when we need to move background so that
+  // it hides user's windows.
+  void Reparent(aura::RootWindow* root_window,
+                int src_container,
+                int dest_container);
+
+  views::Widget* widget() { return widget_; }
+  ui::Layer* layer() { return layer_.get(); }
+
+ private:
+  views::Widget* widget_;
+  scoped_ptr<ui::Layer> layer_;
+
+  DISALLOW_COPY_AND_ASSIGN(DesktopBackgroundWidgetController);
+};
+
+// Window property key, that binds instance of DesktopBackgroundWidgetController
+// to root windows.
+extern const aura::WindowProperty<DesktopBackgroundWidgetController*>* const
+    kWindowDesktopComponent;
+
+}  // namespace internal
+}  // namespace ash
+
+#endif  // ASH_DESKTOP_BACKGROUND_DESKTOP_BACKGROUND_WIDGET_CONTROLLER_H_