Add missing include in the alert xpc service

chrome/browser/ui/cocoa/notifications/xpc_service_main.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 <Foundation/Foundation.h>
+#include <xpc/xpc.h>
 
 #include "base/mac/scoped_nsobject.h"
 #import "chrome/browser/ui/cocoa/notifications/notification_service_delegate.h"
 
 // The main method of the notification alert xpc service.
 // It is initiaized by Chrome on demand whenever a notification of type alert
 // needs to be displayed.
 // The connection will then remain open in order to receive notification
 // clicks and so until all notifications of type alert are closed.
 int main(int argc, const char* argv[]) {
   @autoreleasepool {
     base::scoped_nsobject<ServiceDelegate> delegate(
         [[ServiceDelegate alloc] init]);
 
     NSXPCListener* listener = [NSXPCListener serviceListener];
     listener.delegate = delegate.get();
 
     // Keep the connection open forever since there is no xpc_transaction_end()
     // TODO(miguelg): send xpc_transaction_end when no alerts are being
     // displayed.
     xpc_transaction_begin();
 
     [listener resume];
 
     return 0;
   }
 }