[ObjC ARC] Converts ios/chrome/browser/browser_state:browser_state_impl.

ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm

Index: ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm
diff --git a/ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm b/ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm
index 4a886451306b191717d7ddf5ff569d12d79ce604..4761ccbef43339630ced009f2ba3b8ca9564ed8a 100644
--- a/ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm
+++ b/ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm
@@ -37,6 +37,10 @@
 #include "net/ssl/default_channel_id_store.h"
 #include "net/url_request/url_request_job_factory_impl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Callback doing nothing, called by DoomIncognitoCache() below.