Correct iOS build for latest Xcode beta.

ios/web/shell/view_controller.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.
 
 #import "ios/web/shell/view_controller.h"
 
 #include "base/mac/objc_property_releaser.h"
 #import "base/mac/scoped_nsobject.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/sys_string_conversions.h"
 #include "ios/net/cookies/cookie_store_ios.h"
 #import "ios/net/crn_http_protocol_handler.h"
+#import "ios/net/empty_nsurlcache.h"
 #import "ios/web/navigation/crw_session_controller.h"
 #include "ios/web/navigation/web_load_params.h"
 #import "ios/web/net/crw_url_verifying_protocol_handler.h"
 #include "ios/web/net/request_tracker_factory_impl.h"
 #import "ios/web/net/web_http_protocol_handler_delegate.h"
 #include "ios/web/public/referrer.h"
 #import "ios/web/public/web_controller_factory.h"
 #include "ios/web/public/web_state/web_state.h"
 #include "ios/web/public/web_view_util.h"
 #include "ios/web/shell/shell_browser_state.h"
@@ skipping 100 matching lines @@
   [[_webController view] setFrame:[_containerView bounds]];
   [_containerView addSubview:[_webController view]];
 
   web::WebLoadParams params(GURL("https://dev.chromium.org/"));
   params.transition_type = ui::PAGE_TRANSITION_TYPED;
   [_webController loadWithParams:params];
 }
 
 - (void)setUpNetworkStack {
   // Disable the default cache.
-  [NSURLCache setSharedURLCache:nil];
+  [NSURLCache setSharedURLCache:[EmptyNSURLCache emptyNSURLCache]];
 
   _httpProtocolDelegate.reset(new web::WebHTTPProtocolHandlerDelegate(
       _browserState->GetRequestContext()));
   net::HTTPProtocolHandlerDelegate::SetInstance(_httpProtocolDelegate.get());
   BOOL success = [NSURLProtocol registerClass:[CRNHTTPProtocolHandler class]];
   DCHECK(success);
   // The CRWURLVerifyingProtocolHandler is used to verify URL in the
   // CRWWebController. It must be registered after the HttpProtocolHandler
   // because handlers are called in the reverse order of declaration.
   success =
@@ skipping 181 matching lines @@
 - (void)webDidPrepareForGoBack {
 }
 - (int)downloadImageAtUrl:(const GURL&)url
             maxBitmapSize:(uint32_t)maxBitmapSize
                  callback:
                      (const web::WebState::ImageDownloadCallback&)callback {
   return -1;
 }
 
 @end