[ObjC ARC] Converts ios/web/shell/test to ARC.

ios/web/shell/test/earl_grey/shell_earl_grey.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 "ios/web/shell/test/earl_grey/shell_earl_grey.h"
 
 #import <EarlGrey/EarlGrey.h>
 
 #import "ios/web/public/test/earl_grey/js_test_util.h"
 #include "ios/web/shell/test/app/navigation_test_util.h"
 #import "ios/web/shell/test/app/web_shell_test_util.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 const NSTimeInterval kWaitForPageLoadTimeout = 10.0;
 }  // namespace
 
 @implementation ShellEarlGrey
 
 + (void)loadURL:(const GURL&)URL {
   web::shell_test_util::LoadUrl(URL);
 
   // Make sure that the page started loading.
   GREYAssert(web::shell_test_util::IsLoading(), @"Page did not start loading.");
 
   GREYCondition* condition =
       [GREYCondition conditionWithName:@"Wait for page to complete loading."
                                  block:^BOOL {
                                    return !web::shell_test_util::IsLoading();
                                  }];
   GREYAssert([condition waitWithTimeout:kWaitForPageLoadTimeout],
              @"Page did not complete loading.");
 
   web::WebState* webState = web::shell_test_util::GetCurrentWebState();
   if (webState->ContentIsHTML())
     web::WaitUntilWindowIdInjected(webState);
 }
 
 @end