Separate ash::test::DisplayManagerTestApi from ash

ash/test/ash_test_helper.cc

Index: ash/test/ash_test_helper.cc
diff --git a/ash/test/ash_test_helper.cc b/ash/test/ash_test_helper.cc
index 860bf93d21f3e0053973cd49a26856ed08ec847b..a12d6c64f20a69d492e281dcf64b5c0328283560 100644
--- a/ash/test/ash_test_helper.cc
+++ b/ash/test/ash_test_helper.cc
@@ -137,7 +137,8 @@ void AshTestHelper::SetUp(bool start_session,
     GetTestSessionStateDelegate()->SetHasActiveUser(true);
   }
 
-  test::DisplayManagerTestApi().DisableChangeDisplayUponHostResize();
+  test::DisplayManagerTestApi(Shell::GetInstance()->display_manager())
+      .DisableChangeDisplayUponHostResize();
   ShellTestApi(shell).DisableDisplayAnimator();
 
   test_screenshot_delegate_ = new TestScreenshotDelegate();