[ObjC ARC] Converts ios/chrome/app/spotlight:spotlight to ARC.

ios/chrome/app/spotlight/spotlight_util.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.
 
 #import "ios/chrome/app/spotlight/spotlight_util.h"
 
 #import <CoreSpotlight/CoreSpotlight.h>
 
 #include "base/metrics/histogram_macros.h"
 #include "base/strings/sys_string_conversions.h"
 #include "ios/public/provider/chrome/browser/chrome_browser_provider.h"
 #include "ios/public/provider/chrome/browser/spotlight/spotlight_provider.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // This enum is used for Histogram. Items should not be removed or reordered and
 // this enum should be kept synced with histograms.xml.
 // The three states correspond to:
 // - SPOTLIGHT_UNSUPPORTED: Framework CoreSpotlight is not found and
 // [CSSearchableIndex class] returns nil.
 // - SPOTLIGHT_UNAVAILABLE: Framework is loaded but [CSSearchableIndex
 // isIndexingAvailable] return NO. Note: It is unclear if this state is
 // reachable (I could not find configuration where CoreSpotlight was loaded but
 // [CSSearchableIndex isIndexingAvailable] returned NO.
@@ skipping 182 matching lines @@
       }
     }
     completion(nil);
 
   }];
 
   [query start];
 }
 
 }  // namespace spotlight