[iOS/ARC] Fix a violation of ODR in base::BindBlock under ARC.

ios/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.mm

 // Copyright 2015 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/chrome/browser/browser_state/off_the_record_chrome_browser_state_io_data.h"
 
 #import <UIKit/UIKit.h>
 
 #include <utility>
 
@@ skipping 46 matching lines @@
   handle->DoomIncognitoCache();
 }
 
 }  // namespace
 
 void OffTheRecordChromeBrowserStateIOData::Handle::DoomIncognitoCache() {
   // The cache for the incognito profile is in RAM.
   scoped_refptr<net::URLRequestContextGetter> getter =
       main_request_context_getter_;
   web::WebThread::PostTask(
-      web::WebThread::IO, FROM_HERE, base::BindBlock(^{
+      web::WebThread::IO, FROM_HERE, base::BindBlockArc(^{
         DCHECK_CURRENTLY_ON(web::WebThread::IO);
         net::HttpCache* cache = getter->GetURLRequestContext()
                                     ->http_transaction_factory()
                                     ->GetCache();
         if (!cache->GetCurrentBackend())
           return;
         cache->GetCurrentBackend()->DoomAllEntries(base::Bind(&DoNothing));
       }));
 }
 
@@ skipping 154 matching lines @@
   NOTREACHED();
   return nullptr;
 }
 
 ChromeBrowserStateIOData::AppRequestContext*
 OffTheRecordChromeBrowserStateIOData::AcquireIsolatedAppRequestContext(
     net::URLRequestContext* main_context) const {
   NOTREACHED();
   return nullptr;
 }