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

ash/shell_unittest.cc

Index: ash/shell_unittest.cc
diff --git a/ash/shell_unittest.cc b/ash/shell_unittest.cc
index 3bf6cf396e6a73212c21799e4791a84c0256ed6c..ee8770f365d6b8c996346a2020a5997588ad75de 100644
--- a/ash/shell_unittest.cc
+++ b/ash/shell_unittest.cc
@@ -58,6 +58,8 @@ void ExpectAllContainers() {
   EXPECT_TRUE(Shell::GetContainer(
       root_window, internal::kShellWindowId_SystemModalContainer));
   EXPECT_TRUE(Shell::GetContainer(
+      root_window, internal::kShellWindowId_LockScreenBackgroundContainer));
+  EXPECT_TRUE(Shell::GetContainer(
       root_window, internal::kShellWindowId_LockScreenContainer));
   EXPECT_TRUE(Shell::GetContainer(
       root_window, internal::kShellWindowId_LockSystemModalContainer));