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

ios/chrome/browser/install_time_util.mm

 // Copyright 2013 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/install_time_util.h"
 
 #include <Foundation/Foundation.h>
 #include <stdint.h>
 
 #include "base/mac/foundation_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 NSString* const kInstallationTimeKey = @"omaha.InstallationTime";
 
 // Returns the installation time of the application: this is the time the
 // application was first installed, not the time the last version was installed.
 // If the installation time is unknown, returns a base::Time corresponding to
 // |kUnknownInstallDate|.
 // To be noted: this value is reset if the application is uninstalled.
 base::Time GetNSUserDefaultsInstallationTime() {
@@ skipping 23 matching lines @@
   if (is_first_run)
     return base::Time::Now();
 
   if (ns_user_defaults_install_time.is_null())
     return base::Time::FromTimeT(kUnknownInstallDate);
 
   return ns_user_defaults_install_time;
 }
 
 }  // namespace install_time_util