chromeos: Makes AshTestBase/Helper target mash when appropriate

ash/mus/bridge/wm_shell_mus.h

Index: ash/mus/bridge/wm_shell_mus.h
diff --git a/ash/mus/bridge/wm_shell_mus.h b/ash/mus/bridge/wm_shell_mus.h
index 6894a323316be4715f491079fa2cb8ecb42a80d7..e94d2881fe0840efe39e6198bde17c3a5ccb1bd9 100644
--- a/ash/mus/bridge/wm_shell_mus.h
+++ b/ash/mus/bridge/wm_shell_mus.h
@@ -36,10 +36,13 @@ class WmShellMusTestApi;
 // WmShell implementation for mus.
 class WmShellMus : public WmShell {
  public:
+  // If |create_session_state_delegate_stub| is true SessionStateDelegateStub is
+  // created. If false, the SessionStateDelegate from Shell is used.
   WmShellMus(WmWindow* primary_root_window,
              std::unique_ptr<ShellDelegate> shell_delegate,
              WindowManager* window_manager,
-             views::PointerWatcherEventRouter* pointer_watcher_event_router);
+             views::PointerWatcherEventRouter* pointer_watcher_event_router,
+             bool create_session_state_delegate_stub);
   ~WmShellMus() override;
 
   static WmShellMus* Get();