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 89d2f20a2f3966ede88328fa7163134ac7e9911c..5cf9ec91f4dda65a8390f782e4371dcb542ac72b 100644
--- a/ash/BUILD.gn
+++ b/ash/BUILD.gn
@@ -658,6 +658,8 @@ 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",
@@ -1398,6 +1400,10 @@ 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.