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

ios/chrome/browser/ui/stack_view/stack_view_egtest.mm

Index: ios/chrome/browser/ui/stack_view/stack_view_egtest.mm
diff --git a/ios/chrome/browser/ui/stack_view/stack_view_egtest.mm b/ios/chrome/browser/ui/stack_view/stack_view_egtest.mm
index 20ec6efdb300f1ec0b7385f74dad99476d74881d..ab24504ecf4702b6be59bdc905f215a7889503d0 100644
--- a/ios/chrome/browser/ui/stack_view/stack_view_egtest.mm
+++ b/ios/chrome/browser/ui/stack_view/stack_view_egtest.mm
@@ -25,6 +25,10 @@
 #import "ios/chrome/test/earl_grey/chrome_test_case.h"
 #include "ios/testing/earl_grey/disabled_test_macros.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Returns a GREYMatcher that matches |view|.
 // TODO(crbug.com/642619): Evaluate whether this should be shared code.