[ObjC ARC] Converts ios/chrome/app:app_internal to ARC.

ios/chrome/app/memory_monitor.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/chrome/app/memory_monitor.h"
 
 #include <dispatch/dispatch.h>
 #import <Foundation/NSPathUtilities.h>
 
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/location.h"
 #include "base/logging.h"
 #import "base/mac/foundation_util.h"
 #include "base/strings/sys_string_conversions.h"
 #include "base/sys_info.h"
 #import "ios/chrome/browser/crash_report/breakpad_helper.h"
 #include "ios/web/public/web_thread.h"
 
+#if !defined(__has_feature) || !__has_feature(objc_arc)
+#error "This file requires ARC support."
+#endif
+
 namespace ios_internal {
 
 void AsynchronousFreeMemoryMonitor() {
   UpdateBreakpadMemoryValues();
   web::WebThread::PostDelayedTask(
       web::WebThread::FILE, FROM_HERE,
       base::Bind(&ios_internal::AsynchronousFreeMemoryMonitor),
       base::TimeDelta::FromSeconds(30));
 }
 
 void UpdateBreakpadMemoryValues() {
   int freeMemory =
       static_cast<int>(base::SysInfo::AmountOfAvailablePhysicalMemory() / 1024);
   breakpad_helper::SetCurrentFreeMemoryInKB(freeMemory);
   NSArray* paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory,
                                                        NSUserDomainMask, YES);
   NSString* value = base::mac::ObjCCastStrict<NSString>([paths lastObject]);
   base::FilePath filePath = base::FilePath(base::SysNSStringToUTF8(value));
   int freeDiskSpace =
       static_cast<int>(base::SysInfo::AmountOfFreeDiskSpace(filePath) / 1024);
   breakpad_helper::SetCurrentFreeDiskInKB(freeDiskSpace);
 }
 }