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

ios/chrome/browser/web/child_window_open_by_dom_egtest.mm

 // Copyright 2016 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 <EarlGrey/EarlGrey.h>
 
 #include "base/ios/ios_util.h"
 #include "components/content_settings/core/common/content_settings.h"
 #include "ios/chrome/test/app/settings_test_util.h"
 #import "ios/chrome/test/app/tab_test_util.h"
 #include "ios/chrome/test/app/web_view_interaction_test_util.h"
 #import "ios/chrome/test/earl_grey/chrome_assertions.h"
 #import "ios/chrome/test/earl_grey/chrome_earl_grey.h"
 #import "ios/chrome/test/earl_grey/chrome_matchers.h"
 #import "ios/chrome/test/earl_grey/chrome_test_case.h"
 #import "ios/web/public/test/http_server.h"
 #include "ios/web/public/test/http_server_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 using chrome_test_util::AssertMainTabCount;
 using chrome_test_util::TapWebViewElementWithId;
 using chrome_test_util::WebViewContainingText;
 using web::test::HttpServer;
 
 namespace {
 // Test link text and ids.
 const char kNamedWindowLink[] = "openWindowWithName";
 const char kUnnamedWindowLink[] = "openWindowNoName";
 
@@ skipping 172 matching lines @@
       assertWithMatcher:grey_notNil()];
 
   // Close the second opened window. Check that unnamed window 2 is closed.
   chrome_test_util::CloseTabAtIndex(1);
   TapWebViewElementWithId(kCheckWindow2Link);
   [[EarlGrey selectElementWithMatcher:WebViewContainingText(kWindow2Closed)]
       assertWithMatcher:grey_notNil()];
 }
 
 @end