[ObjC ARC] Converts ios/web:ios_web_inttests to ARC.

ios/web/web_state/navigation_callbacks_inttest.mm

 // Copyright 2017 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.
 
 #include <memory>
 #include <string>
 
 #include "base/memory/ptr_util.h"
 #include "base/strings/stringprintf.h"
 #import "ios/web/public/navigation_item.h"
@@ skipping 491 matching lines @@
   NavigationContext* context = nullptr;
   EXPECT_CALL(*observer_, DidStartNavigation(_))
       .WillOnce(VerifyPostStartedContext(web_state(), url, &context));
   EXPECT_CALL(*observer_, DidStartLoading());
   EXPECT_CALL(*observer_, DidFinishNavigation(_))
       .WillOnce(VerifyPostFinishedContext(web_state(), url, &context));
   EXPECT_CALL(*observer_, DidStopLoading());
 
   // Load request using POST HTTP method.
   web::NavigationManager::WebLoadParams params(url);
-  params.post_data.reset(
-      [[@"foo" dataUsingEncoding:NSUTF8StringEncoding] retain]);
-  params.extra_headers.reset([@{ @"Content-Type" : @"text/html" } retain]);
+  params.post_data.reset([@"foo" dataUsingEncoding:NSUTF8StringEncoding]);
+  params.extra_headers.reset(@{ @"Content-Type" : @"text/html" });
   LoadWithParams(params);
 }
 
 // Tests successful navigation to a new page with post HTTP method.
 TEST_F(NavigationCallbacksTest, RendererInitiatedPostNavigation) {
   const GURL url = HttpServer::MakeUrl("http://chromium.test");
   std::map<GURL, std::string> responses;
   responses[url] = "<form method='post' id='form'></form>";
   web::test::SetUpSimpleHttpServer(responses);
 
@@ skipping 119 matching lines @@
   // delegate does not run callback for ShowRepostFormWarningDialog. Clearing
   // the delegate will allow form resubmission. Remove this workaround (clearing
   // the delegate, once |check_for_repost| is supported).
   web_state()->SetDelegate(nullptr);
   ExecuteBlockAndWaitForLoad(action, ^{
     navigation_manager()->GoForward();
   });
 }
 
 }  // namespace web