chromeos: makes WindowManager not delete shell when connection to mus is lost

ash/mus/window_manager.h

Index: ash/mus/window_manager.h
diff --git a/ash/mus/window_manager.h b/ash/mus/window_manager.h
index 4ac49da18bbf10d9c6ebb7fa2fd6e0546ddbb3fa..8f8631b130d1f85b0c49c0f0e3341d0a24a8cc75 100644
--- a/ash/mus/window_manager.h
+++ b/ash/mus/window_manager.h
@@ -12,6 +12,7 @@
 
 #include "ash/root_window_controller.h"
 #include "ash/shell_delegate.h"
+#include "base/callback_forward.h"
 #include "base/macros.h"
 #include "base/memory/ref_counted.h"
 #include "services/ui/common/types.h"
@@ -74,6 +75,10 @@ class WindowManager : public aura::WindowManagerDelegate,
             const scoped_refptr<base::SequencedWorkerPool>& blocking_pool,
             std::unique_ptr<ash::ShellDelegate> shell_delegate = nullptr);
 
+  // Sets the callback that is run once the connection to mus is lost. If not
+  // set shutdown occurs when the connection is lost (the Shell is deleted).
+  void SetLostConnectionCallback(base::OnceClosure closure);
+
   // Blocks waiting for the initial set of displays.
   bool WaitForInitialDisplays();
 
@@ -197,6 +202,8 @@ class WindowManager : public aura::WindowManagerDelegate,
 
   const Config config_;
 
+  base::OnceClosure lost_connection_callback_;
+
   std::unique_ptr<::wm::WMState> wm_state_;
   std::unique_ptr<aura::PropertyConverter> property_converter_;