cros: Make sure views-based lock screen is destroyed after it is dismissed.

ash/login/ui/lock_screen.cc

Index: ash/login/ui/lock_screen.cc
diff --git a/ash/login/ui/lock_screen.cc b/ash/login/ui/lock_screen.cc
index baaf5bfd80b602c59fc51ead9cfa6aae0027c8f9..245cc77d51e6d1669f5b1c6d67632eb070a32707 100644
--- a/ash/login/ui/lock_screen.cc
+++ b/ash/login/ui/lock_screen.cc
@@ -6,21 +6,37 @@
 
 #include "ash/login/ui/lock_contents_view.h"
 #include "ash/login/ui/lock_window.h"
+#include "components/user_manager/user_manager.h"
 #include "ui/display/display.h"
 #include "ui/display/screen.h"
 #include "ui/views/widget/widget.h"
 
 namespace ash {
 
+namespace {
+// Reference to global lock screen instance. There can only ever be one lock
+// screen display at the same time.
+LockWindow* window_ = nullptr;
+}  // namespace
+
 bool ShowLockScreen() {
-  LockWindow* window = new LockWindow();
-  window->SetBounds(display::Screen::GetScreen()->GetPrimaryDisplay().bounds());
+  CHECK(!window_);
+  window_ = new LockWindow();
+  window_->SetBounds(
+      display::Screen::GetScreen()->GetPrimaryDisplay().bounds());
+
+  auto* contents = new LockContentsView();
 
-  views::View* contents = new LockContentsView();
-  window->SetContentsView(contents);
-  window->Show();
+  window_->SetContentsView(contents);
+  window_->Show();
 
   return true;
 }
 
+void DestroyLockScreen() {
+  CHECK(window_);
+  window_->Close();
+  window_ = nullptr;
+}
+
 }  // namespace ash