Specify a default display UI scale to reset the zoom to

ash/display/cursor_window_controller_unittest.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ash/display/cursor_window_controller.h"
 
 #include "ash/display/display_util.h"
 #include "ash/display/window_tree_host_manager.h"
 #include "ash/shell.h"
 #include "ash/test/ash_test_base.h"
@@ skipping 145 matching lines @@
   UpdateDisplay("1000x500*2");
   int64_t primary_id = display::Screen::GetScreen()->GetPrimaryDisplay().id();
 
   test::ScopedSetInternalDisplayId set_internal(display_manager(), primary_id);
   SetCursorCompositionEnabled(true);
   ASSERT_EQ(
       2.0f,
       display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
   EXPECT_TRUE(GetCursorImage().HasRepresentation(2.0f));
 
-  ASSERT_TRUE(display_manager()->SetDisplayUIScale(primary_id, 2.0f));
+  ASSERT_TRUE(test::DisplayManagerTestApi(display_manager())
+                  .SetDisplayUIScale(primary_id, 2.0f));
   ASSERT_EQ(
       1.0f,
       display::Screen::GetScreen()->GetPrimaryDisplay().device_scale_factor());
   EXPECT_TRUE(GetCursorImage().HasRepresentation(2.0f));
 }
 #endif
 
 }  // namespace ash