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

ios/chrome/browser/web/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>
 
 #import "base/test/ios/wait_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::OmniboxText;
 using chrome_test_util::TapWebViewElementWithId;
 using chrome_test_util::WebViewContainingText;
 using web::test::HttpServer;
 
 namespace {
 const char kTestURL[] =
     "http://ios/testing/data/http_server_files/window_open.html";
 }  // namespace
@@ skipping 29 matching lines @@
 - (void)testLinkWithBlankTargetWithImmediateClose {
   TapWebViewElementWithId("webScenarioWindowOpenBlankTargetWithImmediateClose");
   AssertMainTabCount(1);
 }
 
 // Tests that sessionStorage content is available for windows opened by DOM via
 // target="_blank" links.
 - (void)testLinkWithBlankTargetSessionStorage {
   using chrome_test_util::ExecuteJavaScript;
 
-  NSError* error = nil;
+  __unsafe_unretained NSError* error = nil;
   ExecuteJavaScript(@"sessionStorage.setItem('key', 'value');", &error);
   GREYAssert(!error, @"Error during script execution: %@", error);
 
   TapWebViewElementWithId("webScenarioWindowOpenSameURLWithBlankTarget");
   AssertMainTabCount(2);
   [[EarlGrey selectElementWithMatcher:WebViewContainingText("Expected result")]
       assertWithMatcher:grey_notNil()];
 
   id value = ExecuteJavaScript(@"sessionStorage.getItem('key');", &error);
   GREYAssert(!error, @"Error during script execution: %@", error);
@@ skipping 103 matching lines @@
       assertWithMatcher:grey_notNil()];
 }
 
 // Tests that closing the current window using DOM fails.
 - (void)testCloseWindowNotOpenByDOM {
   TapWebViewElementWithId("webScenarioWindowClose");
   AssertMainTabCount(1);
 }
 
 @end