[ObjC ARC] Converts ios/chrome/common:common to ARC.

ios/chrome/common/channel_info.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/common/channel_info.h"
 
 #include <dispatch/dispatch.h>
 #import <Foundation/Foundation.h>
 
 #import "base/mac/bundle_locations.h"
 #include "base/profiler/scoped_tracker.h"
 #import "base/strings/sys_string_conversions.h"
 #include "components/version_info/version_info.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 #if defined(GOOGLE_CHROME_BUILD)
 // Channel of the running application, initialized by the first call to
 // GetChannel() and cached for the whole application lifetime.
 version_info::Channel g_channel = version_info::Channel::UNKNOWN;
 #endif
 
 }  // namespace
 
@@ skipping 54 matching lines @@
     } else if ([channel isEqualToString:@"canary"]) {
       g_channel = version_info::Channel::CANARY;
     }
   });
 
   return g_channel;
 #else
   return version_info::Channel::UNKNOWN;
 #endif
 }