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

Automatically generated ARCMigrate commit
Notable issues:None
BUG=624363
TEST=None

Review-Url: https://codereview.chromium.org/2514813002
Cr-Commit-Position: refs/heads/master@{#436289}

ios/chrome/browser/metrics/BUILD.gn

@@ -3,6 +3,7 @@
 # found in the LICENSE file.
 
 source_set("metrics") {
+  configs += [ "//build/config/compiler:enable_arc" ]
   sources = [
     "field_trial_synchronizer.cc",
     "field_trial_synchronizer.h",

ios/chrome/browser/metrics/ios_chrome_metrics_services_manager_client.mm

@@ -21,6 +21,10 @@
 #include "ios/chrome/browser/variations/ios_ui_string_overrider_factory.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 void PostStoreMetricsClientInfo(const metrics::ClientInfo& client_info) {}

ios/chrome/browser/metrics/mobile_session_shutdown_metrics_provider.mm

@@ -13,6 +13,10 @@
 #import "ios/chrome/browser/crash_report/crash_report_background_uploader.h"
 #import "ios/chrome/browser/metrics/previous_session_info.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Logs |type| in the shutdown type histogram.

ios/chrome/browser/metrics/previous_session_info.mm

@@ -5,11 +5,14 @@
 #import "ios/chrome/browser/metrics/previous_session_info.h"
 
 #include "base/logging.h"
-#include "base/mac/scoped_nsobject.h"
 #include "base/strings/sys_string_conversions.h"
 #include "components/version_info/version_info.h"
 #import "ios/chrome/browser/metrics/previous_session_info_private.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Key in the NSUserDefaults for a string value that stores the version of the
@@ -63,7 +66,6 @@ static PreviousSessionInfo* gSharedInstance = nil;
 }
 
 + (void)resetSharedInstanceForTesting {
-  [gSharedInstance release];
   gSharedInstance = nil;
 }