[ObjC ARC] Converts ios/chrome/common/app_group:main_app to ARC.

ios/chrome/common/app_group/app_group_metrics_mainapp.mm

Index: ios/chrome/common/app_group/app_group_metrics_mainapp.mm
diff --git a/ios/chrome/common/app_group/app_group_metrics_mainapp.mm b/ios/chrome/common/app_group/app_group_metrics_mainapp.mm
index 3e32438fd322e295241924f4e99039c6e51ce9dd..b33cfec0c983b9108fc545aacda9c8a3d02c24af 100644
--- a/ios/chrome/common/app_group/app_group_metrics_mainapp.mm
+++ b/ios/chrome/common/app_group/app_group_metrics_mainapp.mm
@@ -7,16 +7,18 @@
 #include <stdint.h>
 
 #include "base/logging.h"
-#include "base/mac/scoped_nsobject.h"
 #include "ios/chrome/common/app_group/app_group_constants.h"
 #include "ios/chrome/common/app_group/app_group_metrics.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace app_group {
 
 namespace main_app {
 
-void ProcessPendingLogs(
-    const base::mac::ScopedBlock<ProceduralBlockWithData>& callback) {
+void ProcessPendingLogs(ProceduralBlockWithData callback) {
   NSFileManager* file_manager = [NSFileManager defaultManager];
   NSURL* store_url = [file_manager
       containerURLForSecurityApplicationGroupIdentifier:ApplicationGroup()];
@@ -34,7 +36,7 @@ void ProcessPendingLogs(
           [log_dir_url URLByAppendingPathComponent:pending_log isDirectory:NO];
       if (callback) {
         NSData* log_content = [file_manager contentsAtPath:[file_url path]];
-        callback.get()(log_content);
+        callback(log_content);
       }
       [file_manager removeItemAtURL:file_url error:nil];
     }
@@ -45,8 +47,8 @@ void EnableMetrics(NSString* client_id,
                    NSString* brand_code,
                    int64_t install_date,
                    int64_t enable_metrics_date) {
-  base::scoped_nsobject<NSUserDefaults> shared_defaults(
-      [[NSUserDefaults alloc] initWithSuiteName:ApplicationGroup()]);
+  NSUserDefaults* shared_defaults =
+      [[NSUserDefaults alloc] initWithSuiteName:ApplicationGroup()];
   [shared_defaults setObject:client_id forKey:@(kChromeAppClientID)];
 
   [shared_defaults
@@ -60,8 +62,8 @@ void EnableMetrics(NSString* client_id,
 }
 
 void DisableMetrics() {
-  base::scoped_nsobject<NSUserDefaults> shared_defaults(
-      [[NSUserDefaults alloc] initWithSuiteName:ApplicationGroup()]);
+  NSUserDefaults* shared_defaults =
+      [[NSUserDefaults alloc] initWithSuiteName:ApplicationGroup()];
   [shared_defaults removeObjectForKey:@(kChromeAppClientID)];
 }