Re-reland: chromeos: Fix shelf appearing at login screen under mash

ash/mus/test/wm_test_base.h

Index: ash/mus/test/wm_test_base.h
diff --git a/ash/mus/test/wm_test_base.h b/ash/mus/test/wm_test_base.h
index 24e2c620cc29cde6d10d4ae56a40724a97f298bc..ccdc56ca381ce03222ea9c753dcfdcb8e819a4e6 100644
--- a/ash/mus/test/wm_test_base.h
+++ b/ash/mus/test/wm_test_base.h
@@ -82,6 +82,10 @@ class WmTestBase : public testing::Test {
  private:
   friend class AshTestImplMus;
 
+  // Simulates the first user logging in and the session becoming active.
+  // Classic ash handles this via AshTestHelper and TestSessionStateDelegate.
+  void SimulateUserLogin();
+
   bool setup_called_ = false;
   bool teardown_called_ = false;
   std::unique_ptr<ui::ScopedAnimationDurationScaleMode> zero_duration_mode_;