chromeos: Makes AshTestBase/Helper target mash when appropriate

ui/display/test/display_manager_test_api.cc

Index: ui/display/test/display_manager_test_api.cc
diff --git a/ui/display/test/display_manager_test_api.cc b/ui/display/test/display_manager_test_api.cc
index 16e9a1b8ddb5e971beb82a594aad561c0641476d..0a8078b4ebae0e780d0d40710f8036cfd62dc533 100644
--- a/ui/display/test/display_manager_test_api.cc
+++ b/ui/display/test/display_manager_test_api.cc
@@ -58,7 +58,9 @@ scoped_refptr<ManagedDisplayMode> GetDisplayModeForUIScale(
 }  // namespace
 
 DisplayManagerTestApi::DisplayManagerTestApi(DisplayManager* display_manager)
-    : display_manager_(display_manager) {}
+    : display_manager_(display_manager) {
+  DCHECK(display_manager);
+}
 
 DisplayManagerTestApi::~DisplayManagerTestApi() {}