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

ios/chrome/browser/prefs/browser_prefs.mm

Index: ios/chrome/browser/prefs/browser_prefs.mm
diff --git a/ios/chrome/browser/prefs/browser_prefs.mm b/ios/chrome/browser/prefs/browser_prefs.mm
index 568823b883c782edfbb9b9957163d88e013d64ab..e31dee05215c2c3b64fe928243f7e82222b22a11 100644
--- a/ios/chrome/browser/prefs/browser_prefs.mm
+++ b/ios/chrome/browser/prefs/browser_prefs.mm
@@ -55,6 +55,10 @@
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ui/base/l10n/l10n_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 void RegisterLocalStatePrefs(PrefRegistrySimple* registry) {
   BrowserStateInfoCache::RegisterPrefs(registry);
   flags_ui::PrefServiceFlagsStorage::RegisterPrefs(registry);