cros: Move LockWindow from chrome to ash

ash/login/ui/lock_screen.h

Index: ash/login/ui/lock_screen.h
diff --git a/ash/login/ui/lock_screen.h b/ash/login/ui/lock_screen.h
index 6abe6eb63f44781ad2373de4156e76bf716c471c..fcccca615ae29945b5f6c25c0a8ecbde3d25fc2a 100644
--- a/ash/login/ui/lock_screen.h
+++ b/ash/login/ui/lock_screen.h
@@ -7,16 +7,13 @@
 
 #include "ash/ash_export.h"
 
-namespace views {
-class Widget;
-}
-
 namespace ash {
 
-// Fills the given widget with the lock screen view and displays it.
+// Creates and displays the lock screen. Returns true if the lock screen was
+// displayed.
 //
 // The lock screen communicates with the backend C++ via a mojo API.
-ASH_EXPORT void ShowLockScreenInWidget(views::Widget* widget);
+ASH_EXPORT bool ShowLockScreen();
 
 }  // namespace ash