Correct iOS build for latest Xcode beta.

ios/crnet/crnet_environment.mm

 // Copyright 2014 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 "ios/crnet/crnet_environment.h"
 
 #import <Foundation/Foundation.h>
 
 #include "base/at_exit.h"
 #include "base/command_line.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/files/scoped_file.h"
 #include "base/i18n/icu_util.h"
 #include "base/json/json_writer.h"
 #include "base/mac/bind_objc_block.h"
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_block.h"
 #include "base/path_service.h"
 #include "base/threading/worker_pool.h"
 #import "components/webp_transcode/webp_network_client_factory.h"
 #include "crypto/nss_util.h"
 #include "ios/net/cookies/cookie_store_ios.h"
 #include "ios/net/crn_http_protocol_handler.h"
+#include "ios/net/empty_nsurlcache.h"
 #include "ios/net/request_tracker.h"
 #include "ios/web/public/user_agent.h"
 #include "net/base/net_errors.h"
 #include "net/base/network_change_notifier.h"
 #include "net/base/sdch_manager.h"
 #include "net/cert/cert_verifier.h"
 #include "net/cert_net/nss_ocsp.h"
 #include "net/disk_cache/disk_cache.h"
 #include "net/http/http_auth_handler_factory.h"
 #include "net/http/http_cache.h"
@@ skipping 258 matching lines @@
   net::SetURLRequestContextForNSSHttpIO(nullptr);
 }
 
 net::URLRequestContextGetter* CrNetEnvironment::GetMainContextGetter() {
   return main_context_getter_.get();
 }
 
 void CrNetEnvironment::SetHTTPProtocolHandlerRegistered(bool registered) {
   if (registered) {
     // Disable the default cache.
-    [NSURLCache setSharedURLCache:nil];
+    [NSURLCache setSharedURLCache:[EmptyNSURLCache emptyNSURLCache]];
     // Register the chrome http protocol handler to replace the default one.
     BOOL success = [NSURLProtocol registerClass:[CRNHTTPProtocolHandler class]];
     DCHECK(success);
   } else {
     // Set up an empty default cache, with default size.
     // TODO(droger): If the NSURLCache is to be used, its size should most
     // likely be changed. On an iPod2 with iOS4, the default size is 512k.
     [NSURLCache setSharedURLCache:[[[NSURLCache alloc] init] autorelease]];
     [NSURLProtocol unregisterClass:[CRNHTTPProtocolHandler class]];
   }
@@ skipping 152 matching lines @@
       if (backend)
         backend->DoomAllEntries(client_callback);
   });
   int rc = cache->GetBackend(&backend, doom_callback);
   if (rc != net::ERR_IO_PENDING) {
     // GetBackend doesn't call the callback if it completes synchronously, so
     // call it directly here.
     doom_callback.Run(rc);
   }
 }