[ObjC ARC] Converts ios/chrome/browser/web:web_internal to ARC.

ios/chrome/browser/web/print_observer.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/chrome/browser/web/print_observer.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
-#import "base/mac/scoped_nsobject.h"
 #include "base/values.h"
 #import "ios/chrome/browser/ui/commands/UIKit+ChromeExecuteCommand.h"
 #import "ios/chrome/browser/ui/commands/generic_chrome_command.h"
 #include "ios/chrome/browser/ui/commands/ios_command_ids.h"
 #import "ios/web/public/web_state/web_state.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace {
 // Prefix for print JavaScript command.
 const char kPrintCommandPrefix[] = "print";
 }
 
 PrintObserver::PrintObserver(web::WebState* web_state)
     : web::WebStateObserver(web_state) {
   web_state->AddScriptCommandCallback(
       base::Bind(&PrintObserver::OnPrintCommand, base::Unretained(this)),
       kPrintCommandPrefix);
 }
 
 PrintObserver::~PrintObserver() {
   Detach();
 }
 
 void PrintObserver::WebStateDestroyed() {
   Detach();
 }
 
 bool PrintObserver::OnPrintCommand(const base::DictionaryValue&,
                                    const GURL&,
                                    bool) {
-  base::scoped_nsobject<GenericChromeCommand> print_command(
-      [[GenericChromeCommand alloc] initWithTag:IDC_PRINT]);
+  GenericChromeCommand* print_command =
+      [[GenericChromeCommand alloc] initWithTag:IDC_PRINT];
   [web_state()->GetView() chromeExecuteCommand:print_command];
   return true;
 }
 
 void PrintObserver::Detach() {
   if (web_state()) {
     web_state()->RemoveScriptCommandCallback(kPrintCommandPrefix);
   }
 }