chromeos: Fix shelf appearing at login screen under mash

ash/mus/test/ash_test_impl_mus.h

Index: ash/mus/test/ash_test_impl_mus.h
diff --git a/ash/mus/test/ash_test_impl_mus.h b/ash/mus/test/ash_test_impl_mus.h
index 1f62ab3cb9c676d9cb86aae745e501c5b3266994..1f6c9c1faf8d40f324da64df2da369cced7ee315 100644
--- a/ash/mus/test/ash_test_impl_mus.h
+++ b/ash/mus/test/ash_test_impl_mus.h
@@ -42,6 +42,10 @@ class AshTestImplMus : public AshTestImpl {
   void AddTransientChild(WmWindow* parent, WmWindow* window) override;
 
  private:
+  // Simulates the first user logging in and the session becoming active.
+  // Classic ash handles this via AshTestHelper and TestSessionStateDelegate.
+  void SimulateUserLogin();
+
   // TODO(sky): fold WmTestBase directly into this class when no more subclasses
   // of WmTestBase.
   std::unique_ptr<WmTestBase> wm_test_base_;