[ObjC ARC] Converts ios/chrome/app/application_delegate:application_delegate_internal to ARC.

ios/chrome/app/application_delegate/metrics_mediator.mm

Index: ios/chrome/app/application_delegate/metrics_mediator.mm
diff --git a/ios/chrome/app/application_delegate/metrics_mediator.mm b/ios/chrome/app/application_delegate/metrics_mediator.mm
index 074ff8fc2a82c280642aff2138f4664520ca87f4..c5954f0ff7f73717209d2b68dc11a20e8967be62 100644
--- a/ios/chrome/app/application_delegate/metrics_mediator.mm
+++ b/ios/chrome/app/application_delegate/metrics_mediator.mm
@@ -4,7 +4,6 @@
 
 #import "ios/chrome/app/application_delegate/metrics_mediator.h"
 
-#include "base/ios/weak_nsobject.h"
 #include "base/mac/bind_objc_block.h"
 #include "base/metrics/user_metrics_action.h"
 #include "base/strings/sys_string_conversions.h"
@@ -240,16 +239,14 @@ using metrics_mediator::kAppEnteredBackgroundDateKey;
   // If metrics are enabled, process the logs. Otherwise, just delete them.
   base::mac::ScopedBlock<app_group::ProceduralBlockWithData> callback;
   if (enabled) {
-    callback.reset(
-        ^(NSData* log_content) {
-          std::string log(static_cast<const char*>([log_content bytes]),
-                          static_cast<size_t>([log_content length]));
-          web::WebThread::PostTask(web::WebThread::UI, FROM_HERE,
-                                   base::BindBlock(^{
-                                     metrics->PushExternalLog(log);
-                                   }));
-        },
-        base::scoped_policy::RETAIN);
+    callback.reset([^(NSData* log_content) {
+      std::string log(static_cast<const char*>([log_content bytes]),
+                      static_cast<size_t>([log_content length]));
+      web::WebThread::PostTask(web::WebThread::UI, FROM_HERE,
+                               base::BindBlockArc(^{
+                                 metrics->PushExternalLog(log);
+                               }));
+    } copy]);
   }
 
   web::WebThread::PostTask(