[ObjC ARC] Converts ios/web:ios_web_general_unittests to ARC.

ios/web/history_state_util_unittest.mm

 // Copyright 2012 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/web/history_state_util.h"
 
 #include <stddef.h>
 
 #include "base/macros.h"
 #include "testing/gtest/include/gtest/gtest.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 web {
 namespace {
 struct TestEntry {
   std::string fromUrl;
   std::string toUrl;
   std::string expectedUrl;
 };
 
 class HistoryStateUtilTest : public ::testing::Test {
  protected:
@@ skipping 77 matching lines @@
   GURL baseUrl("http://not a url");
   std::string destination = "baz";
 
   GURL result = history_state_util::GetHistoryStateChangeUrl(fromUrl, baseUrl,
                                                              destination);
   EXPECT_FALSE(result.is_valid());
 }
 
 }  // anonymous namespace
 }  // namespace web