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

ios/web/webui/mojo_facade.mm

 // Copyright 2016 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/webui/mojo_facade.h"
 
 #import <Foundation/Foundation.h>
 
 #include "base/ios/block_types.h"
 #include "base/json/json_reader.h"
@@ skipping 231 matching lines @@
 
 std::unique_ptr<base::Value> MojoFacade::HandleSupportWatch(
     const base::DictionaryValue* args) {
   int handle = 0;
   CHECK(args->GetInteger("handle", &handle));
   int signals = 0;
   CHECK(args->GetInteger("signals", &signals));
   int callback_id;
   CHECK(args->GetInteger("callbackId", &callback_id));
 
-  mojo::Watcher::ReadyCallback callback = base::BindBlock(^(MojoResult result) {
+  mojo::Watcher::ReadyCallback callback = base::BindBlockArc(^(
+      MojoResult result) {
     NSString* script =
         [NSString stringWithFormat:@"__crWeb.mojo.signalWatch(%d, %d)",
                                    callback_id, result];
     [script_evaluator_ executeJavaScript:script completionHandler:nil];
   });
 
   mojo::Watcher& watcher = watchers_[++last_watch_id_];
   watcher.Start(static_cast<mojo::Handle>(handle), signals, callback);
   return ValueFromInteger(last_watch_id_);
 }
 
 std::unique_ptr<base::Value> MojoFacade::HandleSupportCancelWatch(
     const base::DictionaryValue* args) {
   int watch_id = 0;
   CHECK(args->GetInteger("watchId", &watch_id));
   watchers_.erase(watch_id);
   return nullptr;
 }
 
 }  // namespace web