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

ios/web/web_state/navigation_context_impl_unittest.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.
 
 #import "ios/web/web_state/navigation_context_impl.h"
 
 #import "ios/web/public/test/fakes/test_web_state.h"
 #include "net/http/http_response_headers.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "testing/platform_test.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace web {
 namespace {
 const char kRawResponseHeaders[] =
     "HTTP/1.1 200 OK\0"
     "Content-Length: 450\0"
     "Connection: keep-alive\0";
 }  // namespace
 
 // Test fixture for NavigationContextImplTest testing.
 class NavigationContextImplTest : public PlatformTest {
@@ skipping 45 matching lines @@
   EXPECT_NE(response_headers_.get(), context->GetResponseHeaders());
 
   // SetPost
   context->SetIsPost(true);
   EXPECT_TRUE(context->IsSameDocument());
   ASSERT_TRUE(context->IsPost());
   EXPECT_FALSE(context->GetError());
   EXPECT_NE(response_headers_.get(), context->GetResponseHeaders());
 
   // SetErrorPage
-  NSError* error = [[[NSError alloc] init] autorelease];
+  NSError* error = [[NSError alloc] init];
   context->SetError(error);
   EXPECT_TRUE(context->IsSameDocument());
   ASSERT_TRUE(context->IsPost());
   EXPECT_EQ(error, context->GetError());
   EXPECT_NE(response_headers_.get(), context->GetResponseHeaders());
 
   // SetResponseHeaders
   context->SetResponseHeaders(response_headers_);
   EXPECT_TRUE(context->IsSameDocument());
   ASSERT_TRUE(context->IsPost());
   EXPECT_EQ(error, context->GetError());
   EXPECT_EQ(response_headers_.get(), context->GetResponseHeaders());
 }
 
 }  // namespace web