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

ash/desktop_background/desktop_background_widget_controller.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_widget_controller.h"
+
+#include "ui/aura/root_window.h"
+#include "ui/views/widget/widget.h"
+
+DECLARE_WINDOW_PROPERTY_TYPE(ash::internal::DesktopBackgroundWidgetController*);
+
+namespace ash {
+namespace internal {
+
+DEFINE_OWNED_WINDOW_PROPERTY_KEY(DesktopBackgroundWidgetController,
+                                 kWindowDesktopComponent, NULL);
+
+DesktopBackgroundWidgetController::DesktopBackgroundWidgetController(
+    views::Widget* widget) : widget_(widget) {
+}
+
+DesktopBackgroundWidgetController::DesktopBackgroundWidgetController(
+    ui::Layer* layer) : widget_(NULL) {
+  layer_.reset(layer);
+}
+

[bshe, 2012/07/30 21:38:20]

nit: remove the extra line here.

+
+DesktopBackgroundWidgetController::~DesktopBackgroundWidgetController() {
+  if (widget_) {
+    widget_->CloseNow();
+    widget_ = NULL;
+  } else if (layer_.get())
+    layer_.reset(NULL);
+}
+
+void DesktopBackgroundWidgetController::SetBounds(gfx::Rect bounds) {
+  if (widget_)
+    widget_->SetBounds(bounds);
+  else if (layer_.get())
+    layer_->SetBounds(bounds);
+}
+
+
+void DesktopBackgroundWidgetController::Reparent(aura::RootWindow* root_window,
+                                                 int src_container,
+                                                 int dest_container) {
+  if (widget_) {
+    views::Widget::ReparentNativeView(widget_->GetNativeView(),
+        root_window->GetChildById(dest_container));
+  } else if (layer_.get()) {
+    ui::Layer* layer = layer_.get();
+    root_window->GetChildById(src_container)->layer()->Remove(layer);
+    root_window->GetChildById(dest_container)->layer()->Add(layer);
+  }
+}
+
+}  // namespace internal
+}  // namespace ash