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

ios/web/active_state_manager_impl_unittest.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/web/active_state_manager_impl.h"
 
 #include "ios/web/public/active_state_manager.h"
 #include "ios/web/public/browser_state.h"
 #include "ios/web/public/test/fakes/test_browser_state.h"
 #include "ios/web/public/test/test_web_thread_bundle.h"
 #include "ios/web/public/test/web_test.h"
 #include "testing/gmock/include/gmock/gmock.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 namespace {
 
 // A test fixture to test ActiveStateManagerImpl.
 typedef WebTest ActiveStateManagerImplTest;
 
 // An ActiveStateManager::Observer used for testing purposes.
 class ActiveStateManagerObserver : public ActiveStateManager::Observer {
  public:
   ActiveStateManagerObserver() {}
@@ skipping 45 matching lines @@
   EXPECT_CALL(observer, WillBeDestroyed()).Times(1);
 
   active_state_manager->SetActive(true);
   active_state_manager->SetActive(false);
   // There is no need to explicitly remove the observer since it is removed when
   // |active_state_manager| goes away -- which happens when |browser_state| goes
   // away.
 }
 
 }  // namespace web