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

ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.mm

Index: ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.mm
diff --git a/ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.mm b/ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.mm
index 49dbd24bc22fdcbcd4e9b0ebdbf1c2448432d949..688f89e5355c0159e781d2dacc01b6d62a546f12 100644
--- a/ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.mm
+++ b/ios/chrome/browser/ui/bookmarks/bookmark_promo_controller.mm
@@ -6,7 +6,6 @@
 
 #include <memory>
 
-#include "base/mac/scoped_nsobject.h"
 #include "base/metrics/histogram_macros.h"
 #include "base/metrics/user_metrics.h"
 #include "components/pref_registry/pref_registry_syncable.h"
@@ -20,6 +19,10 @@
 #import "ios/chrome/browser/ui/commands/show_signin_command.h"
 #import "ios/chrome/browser/ui/ui_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Enum is used to record the actions performed by the user on the promo cell.
 // |Stars.PromoActions|.
@@ -86,8 +89,7 @@ class SignInObserver : public SigninManagerBase::Observer {
   }
 
  private:
-  // Weak
-  BookmarkPromoController* controller_;
+  __weak BookmarkPromoController* controller_;
 };
 }  // namespace
 
@@ -128,7 +130,6 @@ class SignInObserver : public SigninManagerBase::Observer {
         ios::SigninManagerFactory::GetForBrowserState(_browserState);
     signinManager->RemoveObserver(_signinObserver.get());
   }
-  [super dealloc];
 }
 
 - (void)showSignIn {
@@ -137,10 +138,10 @@ class SignInObserver : public SigninManagerBase::Observer {
                             BOOKMARKS_PROMO_ACTION_COUNT);
   base::RecordAction(
       base::UserMetricsAction("Signin_Signin_FromBookmarkManager"));
-  base::scoped_nsobject<ShowSigninCommand> command([[ShowSigninCommand alloc]
+  ShowSigninCommand* command = [[ShowSigninCommand alloc]
       initWithOperation:AUTHENTICATION_OPERATION_SIGNIN
       signInAccessPoint:signin_metrics::AccessPoint::
-                            ACCESS_POINT_BOOKMARK_MANAGER]);
+                            ACCESS_POINT_BOOKMARK_MANAGER];
   [self chromeExecuteCommand:command];
 }