[ObjC ARC] Reland of 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 2ceb5e1c4703ebbff3448fa3d040362ece5522c2..238456844a0859bd8f40a39b241afca7fc847dbe 100644
--- a/ios/chrome/browser/ui/uikit_ui_util.mm
+++ b/ios/chrome/browser/ui/uikit_ui_util.mm
@@ -15,7 +15,6 @@
 #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"
@@ -24,6 +23,10 @@
 #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 {
 
 // Linearly interpolate between |a| and |b| by fraction |f|. Satisfies
@@ -552,8 +555,8 @@ void ApplyVisualConstraintsWithMetricsAndOptions(
     NSDictionary* subviewsDictionary,
     NSDictionary* metrics,
     NSLayoutFormatOptions options) {
-  base::scoped_nsobject<NSMutableArray> layoutConstraints(
-      [[NSMutableArray arrayWithCapacity:constraints.count * 3] retain]);
+  NSMutableArray* layoutConstraints =
+      [NSMutableArray arrayWithCapacity:constraints.count * 3];
   for (NSString* constraint in constraints) {
     DCHECK([constraint isKindOfClass:[NSString class]]);
     [layoutConstraints addObjectsFromArray: