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

ios/chrome/browser/chrome_url_util_unittest.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.
 
 #import "ios/chrome/browser/chrome_url_util.h"
 
 #include "base/macros.h"
 #include "base/strings/sys_string_conversions.h"
 #include "ios/chrome/browser/chrome_url_constants.h"
 #import "net/base/mac/url_conversions.h"
 #import "testing/gtest_mac.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 TEST(ChromeURLUtilTest, TestIsExternalFileReference) {
   GURL external_url("chrome://external-file/foo/bar");
   GURL not_external_url("chrome://foo/bar");
   GURL still_not_external_url("http://external-file/foo/bar");
   EXPECT_TRUE(UrlIsExternalFileReference(external_url));
   EXPECT_FALSE(UrlIsExternalFileReference(not_external_url));
   EXPECT_FALSE(UrlIsExternalFileReference(still_not_external_url));
 }
@@ skipping 35 matching lines @@
 
   // Verifies that Chrome scheme can be reset for testing.
   [constants setCallbackSchemeForTesting:@"blah"];
   EXPECT_NSEQ(@"blah", [constants getBundleURLScheme]);
 
   // Resets state in case of further tests.
   [constants setCallbackSchemeForTesting:originalScheme];
 }
 
 }  // namespace