chromeos: converts TopLevelWindowFactoryTest to AshTestBase

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 a9fe837d750b16d8eee23ad86578dabc3a13ae45..57d10d05082ca0990f9283fc7dfc6abcf05a763d 100644
--- a/ash/mus/test/wm_test_base.h
+++ b/ash/mus/test/wm_test_base.h
@@ -62,11 +62,6 @@ class WmTestBase : public testing::Test {
   aura::Window* CreateTestWindow(const gfx::Rect& bounds,
                                  ui::wm::WindowType window_type);
 
-  // Creates a visibile fullscreen top level window on the display corresponding
-  // to the display_id provided.
-  aura::Window* CreateFullscreenTestWindow(
-      int64_t display_id = display::kInvalidDisplayId);
-
   // Creates a window parented to |parent|. The returned window is visible.
   aura::Window* CreateChildTestWindow(aura::Window* parent,
                                       const gfx::Rect& bounds);