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

ios/chrome/browser/web/browsing_prevent_default_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>
 #import <UIKit/UIKit.h>
 #import <XCTest/XCTest.h>
 
 #include "base/strings/sys_string_conversions.h"
 #include "components/content_settings/core/browser/host_content_settings_map.h"
 #include "ios/chrome/browser/browser_state/chrome_browser_state.h"
 #include "ios/chrome/browser/content_settings/host_content_settings_map_factory.h"
 #import "ios/chrome/test/app/chrome_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"
 #include "url/url_constants.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Timeout to use when waiting for a condition to be true.
 const CFTimeInterval kConditionTimeout = 4.0;
 
 // Returns the URL for the HTML that is used for testing purposes in this file.
 GURL GetTestUrl() {
   return web::test::HttpServer::MakeUrl(
       "http://ios/testing/data/http_server_files/"
       "browsing_prevent_default_test_page.html");
@@ skipping 131 matching lines @@
       conditionWithName:@"Wait for navigation to about:blank"
                   block:^BOOL {
                     const GURL& currentURL =
                         chrome_test_util::GetCurrentWebState()->GetVisibleURL();
                     return currentURL == GURL(url::kAboutBlankURL);
                   }] waitWithTimeout:kConditionTimeout];
   chrome_test_util::AssertMainTabCount(1U);
 }
 
 @end