[ObjC ARC] Converts ios/chrome/browser/ui:unit_tests to ARC.

ios/chrome/browser/ui/file_locations_unittest.mm

Index: ios/chrome/browser/ui/file_locations_unittest.mm
diff --git a/ios/chrome/browser/ui/file_locations_unittest.mm b/ios/chrome/browser/ui/file_locations_unittest.mm
index 7c0c0b25617f22df6b1aa065eaec5a196b82273b..cb315b77b049326afe54181cb562588504ec75df 100644
--- a/ios/chrome/browser/ui/file_locations_unittest.mm
+++ b/ios/chrome/browser/ui/file_locations_unittest.mm
@@ -9,6 +9,10 @@
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 extern std::string GetLocalizedFileName(const std::string& base_name,
                                         const std::string& locale,
                                         const std::string& ext);