[cros Aura] Added modal container for screen lock.

ui/aura_shell/shell.cc

Index: ui/aura_shell/shell.cc
diff --git a/ui/aura_shell/shell.cc b/ui/aura_shell/shell.cc
index 49e515ffa687b32e8f8ebdd365e1b82c4434cc6e..3e42cdcf65dca246bc21dfdd0418e186cb16d0a6 100644
--- a/ui/aura_shell/shell.cc
+++ b/ui/aura_shell/shell.cc
@@ -83,6 +83,14 @@ void CreateSpecialContainers(aura::Window::Windows* containers) {
   lock_container->set_id(internal::kShellWindowId_LockScreenContainer);
   containers->push_back(lock_container);
 
+  aura::Window* lock_modal_container = new aura::Window(NULL);
+  lock_modal_container->SetEventFilter(
+      new ToplevelWindowEventFilter(lock_modal_container));
+  lock_modal_container->SetLayoutManager(
+      new internal::ModalContainerLayoutManager(lock_modal_container));
+  lock_modal_container->set_id(internal::kShellWindowId_LockModalContainer);
+  containers->push_back(lock_modal_container);
+
   aura::Window* status_container = new aura::Window(NULL);
   status_container->set_id(internal::kShellWindowId_StatusContainer);
   containers->push_back(status_container);