Introduce window container to be used by lock screen app windows

ash/BUILD.gn

Index: ash/BUILD.gn
diff --git a/ash/BUILD.gn b/ash/BUILD.gn
index 63d90aeaac4d4afc14b13ff509f22b7e4556588b..94036bb1fe8eb365aafdb0f934aaffb2e73246c6 100644
--- a/ash/BUILD.gn
+++ b/ash/BUILD.gn
@@ -653,6 +653,8 @@ component("ash") {
     "wm/immersive_gesture_handler_aura.h",
     "wm/immersive_handler_factory_ash.cc",
     "wm/immersive_handler_factory_ash.h",
+    "wm/lock_action_handler_layout_manager.cc",
+    "wm/lock_action_handler_layout_manager.h",
     "wm/lock_layout_manager.cc",
     "wm/lock_layout_manager.h",
     "wm/lock_state_controller.cc",
@@ -1396,6 +1398,10 @@ test("ash_unittests") {
 
     # TODO: fails because keyboard is not enabled in mash.
     # http://crbug.com/648733.
+    "wm/lock_action_handler_layout_manager_unittest.cc",
+
+    # TODO: fails because keyboard is not enabled in mash.
+    # http://crbug.com/648733.
     "wm/lock_layout_manager_unittest.cc",
 
     # TODO: investigate failures in mash. http://crbug.com/698092.