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

ios/chrome/browser/snapshots/snapshots_util_unittest.mm

 // Copyright 2011 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/snapshots/snapshots_util.h"
 
 #import <Foundation/Foundation.h>
 #import <UIKit/UIKit.h>
 
 #include "base/ios/ios_util.h"
 #include "base/mac/foundation_util.h"
 #include "base/path_service.h"
 #include "base/strings/sys_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 bool RegexMatchesOneSnapshotPath(NSString* regexString) {
   NSRegularExpression* regex =
       [NSRegularExpression regularExpressionWithPattern:regexString
                                                 options:0
                                                   error:nullptr];
   std::vector<base::FilePath> snapshotsPaths;
   GetSnapshotsPaths(&snapshotsPaths);
   int numberOfMatches = 0;
@@ skipping 19 matching lines @@
   NSString* filename = @"UIApplicationAutomaticSnapshotDefault-LandscapeRight";
   NSString* regex = [NSString
       stringWithFormat:@".*/%@/%@%@.png$", path, filename, scaleModifier];
   EXPECT_FALSE(RegexMatchesOneSnapshotPath(@".*"));
   EXPECT_FALSE(RegexMatchesOneSnapshotPath(@"foo"));
   EXPECT_TRUE(RegexMatchesOneSnapshotPath(@".*LandscapeRight.*"));
   EXPECT_TRUE(RegexMatchesOneSnapshotPath(regex));
 }
 
 }  // anonymous namespace