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

ios/chrome/browser/ui/uikit_ui_util.mm

Index: ios/chrome/browser/ui/uikit_ui_util.mm
diff --git a/ios/chrome/browser/ui/uikit_ui_util.mm b/ios/chrome/browser/ui/uikit_ui_util.mm
index 238456844a0859bd8f40a39b241afca7fc847dbe..2ceb5e1c4703ebbff3448fa3d040362ece5522c2 100644
--- a/ios/chrome/browser/ui/uikit_ui_util.mm
+++ b/ios/chrome/browser/ui/uikit_ui_util.mm
@@ -15,6 +15,7 @@
 #include "base/ios/ios_util.h"
 #include "base/logging.h"
 #include "base/mac/foundation_util.h"
+#include "base/mac/scoped_nsobject.h"
 #include "ios/chrome/browser/experimental_flags.h"
 #include "ios/chrome/browser/ui/ui_util.h"
 #include "ios/web/public/web_thread.h"
@@ -22,10 +23,6 @@
 #include "ui/base/l10n/l10n_util_mac.h"
 #include "ui/gfx/ios/uikit_util.h"
 #include "ui/gfx/scoped_cg_context_save_gstate_mac.h"
-
-#if !defined(__has_feature) || !__has_feature(objc_arc)
-#error "This file requires ARC support."
-#endif
 
 namespace {
 
@@ -555,8 +552,8 @@
     NSDictionary* subviewsDictionary,
     NSDictionary* metrics,
     NSLayoutFormatOptions options) {
-  NSMutableArray* layoutConstraints =
-      [NSMutableArray arrayWithCapacity:constraints.count * 3];
+  base::scoped_nsobject<NSMutableArray> layoutConstraints(
+      [[NSMutableArray arrayWithCapacity:constraints.count * 3] retain]);
   for (NSString* constraint in constraints) {
     DCHECK([constraint isKindOfClass:[NSString class]]);
     [layoutConstraints addObjectsFromArray: