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

ios/chrome/browser/ui/browser_otr_state.mm

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ios/chrome/browser/ui/browser_otr_state.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
+
 bool IsOffTheRecordSessionActive() {
   ios::ChromeBrowserProvider* chrome_browser_provider =
       ios::GetChromeBrowserProvider();
   return chrome_browser_provider &&
          chrome_browser_provider->IsOffTheRecordSessionActive();
 }