[ObjC ARC] Converts ios/web/public/test/fakes:fakes to ARC.

ios/web/public/test/fakes/crw_test_web_state_observer.mm

 // Copyright 2017 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/web/public/test/fakes/crw_test_web_state_observer.h"
 
 #include "base/memory/ptr_util.h"
 #import "ios/web/public/web_state/navigation_context.h"
 #import "ios/web/web_state/navigation_context_impl.h"
 #include "net/http/http_response_headers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 TestFormActivityInfo::TestFormActivityInfo() {}
 TestFormActivityInfo::~TestFormActivityInfo() = default;
 TestUpdateFaviconUrlCandidatesInfo::TestUpdateFaviconUrlCandidatesInfo() {}
 TestUpdateFaviconUrlCandidatesInfo::~TestUpdateFaviconUrlCandidatesInfo() =
     default;
 }
 
 @implementation CRWTestWebStateObserver {
   // Arguments passed to |webState:didStartNavigation:|.
@@ skipping 222 matching lines @@
   _stopLoadingInfo = base::MakeUnique<web::TestStopLoadingInfo>();
   _stopLoadingInfo->web_state = webState;
 }
 
 - (void)webStateDidStartLoading:(web::WebState*)webState {
   _startLoadingInfo = base::MakeUnique<web::TestStartLoadingInfo>();
   _startLoadingInfo->web_state = webState;
 }
 
 @end