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

ios/chrome/browser/device_sharing/handoff_manager_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 <XCTest/XCTest.h>
 
 #import "components/handoff/handoff_manager.h"
 #import "ios/chrome/browser/device_sharing/device_sharing_manager.h"
 #include "ios/chrome/browser/ui/ui_util.h"
 #import "ios/chrome/test/app/chrome_test_util.h"
 #import "ios/chrome/test/app/tab_test_util.h"
 #import "ios/chrome/test/earl_grey/chrome_earl_grey.h"
 #import "ios/chrome/test/earl_grey/chrome_test_case.h"
 #include "ios/web/public/test/http_server.h"
 #include "ios/web/public/test/http_server_util.h"
 #import "net/base/mac/url_conversions.h"
 #include "url/gurl.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 
 // Checks that Handoff will report the specified |gurl|.
 void AssertHandoffURL(const GURL& gurl) {
   HandoffManager* manager =
       [chrome_test_util::GetDeviceSharingManager() handoffManager];
   GREYAssertTrue(manager != nil, @"Handoff Manager should not be nil");
   if (gurl.is_valid()) {
     NSURL* URL = net::NSURLWithGURL(gurl);
     GREYAssertTrue([manager.userActivityWebpageURL isEqual:URL],
@@ skipping 106 matching lines @@
   AssertHandoffURL(GURL());
 
   // Loads page three in a new normal tab and verify that Handoff URL is not
   // nil.
   chrome_test_util::OpenNewTab();
   [ChromeEarlGrey loadURL:tab3URL];
   AssertHandoffURL(tab3URL);
 }
 
 @end