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

ios/chrome/browser/ui/external_file_remover.mm

Index: ios/chrome/browser/ui/external_file_remover.mm
diff --git a/ios/chrome/browser/ui/external_file_remover.mm b/ios/chrome/browser/ui/external_file_remover.mm
index b81a45474a71496ffb116933d9b946ed7c28e1ab..90c8efbeea5e8c152171dd22bd5e4cb3ba6df89b 100644
--- a/ios/chrome/browser/ui/external_file_remover.mm
+++ b/ios/chrome/browser/ui/external_file_remover.mm
@@ -13,6 +13,10 @@
 #import "ios/chrome/browser/ui/external_file_controller.h"
 #include "ios/web/public/web_thread.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 ExternalFileRemover::ExternalFileRemover(BrowserViewController* bvc)
     : tabRestoreService_(NULL), bvc_(bvc), weak_ptr_factory_(this) {}
 
@@ -68,7 +72,7 @@ void ExternalFileRemover::RemoveFiles(bool all_files,
     callback_wrapper = base::Bind(&base::DoNothing);
   }
   web::WebThread::PostBlockingPoolTaskAndReply(
-      FROM_HERE, base::BindBlock(^{
+      FROM_HERE, base::BindBlockArc(^{
         [ExternalFileController removeFilesExcluding:referencedFiles
                                            olderThan:ageInDays];
       }),
@@ -84,7 +88,7 @@ void ExternalFileRemover::RemoveAfterDelay(const base::TimeDelta& delay,
   // make sure a method on |this| is not called when the object has gone away.
   base::WeakPtr<ExternalFileRemover> weak_this = weak_ptr_factory_.GetWeakPtr();
   web::WebThread::PostDelayedTask(
-      web::WebThread::UI, FROM_HERE, base::BindBlock(^{
+      web::WebThread::UI, FROM_HERE, base::BindBlockArc(^{
         if (weak_this) {
           weak_this->Remove(remove_all_files, callback_copy);
         } else if (!callback_copy.is_null()) {