Converts ios/web/net to ARC.

ios/web/net/request_tracker_impl.mm

Index: ios/web/net/request_tracker_impl.mm
diff --git a/ios/web/net/request_tracker_impl.mm b/ios/web/net/request_tracker_impl.mm
index d49ba4309e955fb9b07be73fc3a903b46c096d65..fc634e11168de3922187ff0a997aa31085ec1de4 100644
--- a/ios/web/net/request_tracker_impl.mm
+++ b/ios/web/net/request_tracker_impl.mm
@@ -33,6 +33,10 @@
 #include "net/http/http_response_headers.h"
 #include "net/url_request/url_request.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 struct EqualNSStrings {
@@ -254,7 +258,7 @@ struct TrackerCounts {
 }
 
 - (void)errorCallback:(BOOL)flag {
-  base::scoped_nsobject<CRWSSLCarrier> scoped([self retain]);
+  base::scoped_nsobject<CRWSSLCarrier> scoped(self);
   web::WebThread::PostTask(web::WebThread::IO, FROM_HERE,
                            base::Bind(&web::RequestTrackerImpl::ErrorCallback,
                                       tracker_, scoped, flag));
@@ -368,7 +372,7 @@ RequestTrackerImpl::CreateTrackerForRequestGroupID(
 
 void RequestTrackerImpl::StartPageLoad(const GURL& url, id user_info) {
   DCHECK_CURRENTLY_ON(web::WebThread::UI);
-  base::scoped_nsobject<id> scoped_user_info([user_info retain]);
+  base::scoped_nsobject<id> scoped_user_info(user_info);
   web::WebThread::PostTask(
       web::WebThread::IO, FROM_HERE,
       base::Bind(&RequestTrackerImpl::TrimToURL, this, url, scoped_user_info));
@@ -1227,7 +1231,7 @@ void RequestTrackerImpl::TrimToURL(const GURL& full_url, id user_info) {
 
   has_mixed_content_ = new_url_has_mixed_content;
   page_url_ = url;
-  user_info_.reset([user_info retain]);
+  user_info_.reset(user_info);
   estimate_start_index_ = 0;
   is_loading_ = true;
   previous_estimate_ = 0.0f;